If I had the 9 grand handy for the Comptech, I'd put it in my auto. If the tranny went, I'd just replace it. I'm very dubious regarding the whole "can't handle 290hp" argument. I just really don't believe that.
Either way, adding a more efficient TC shouldnt stress the tranny, I dont think... Literally everyone adds TCs and better gearing on LS1s.
I've noticed a lot more posts regarding automatic transmissions lately. Reading them and the conjecturing and theories behind the NSX auto tranny weak spots, etc brought back a lot of good memories. I'm surprised no transmission engineer ever posted on Prime? Or I may have missed those posts if so. I was an automatic transmission engineer for Ford for 9 years. But I was a knuckle-dragging gearset engineer and not a calibrator - a calibrator programs how the pumps, solenoids, clutches, bands, etc, perform and know how the transmisison "thinks," they would be good diagnosticians for figuring out various tranny problems I read here, like lost 2nd gears and flared shifts. For those - first thing I'd check is your transmission fluid - read your manual - should do it when the engine is running. Check that it's red and smells "OK" and is not brown and burnt. If it's burnt/foul smelling and dark brown that's a good sign that you may have burnt clutch(es) and/or contamination in your fluid which could cause your hydraulics to not act properly. It takes just one slightly oversize piece of contamination to cause stuck solenoids, failed bearings and seals, or leaky solenoids or clutches, in many cases losing pressure to clutches or bands and causing flared shifts, lost shifts, etc. I assume the NSX auto tranny is like many 4-speeds where 3rd gear is 1:1, which is why many transmissions that lose 1st or 2nd gear still seem to work OK in 3rd because there's no relative movement of planetary gears thru the trans body, maybe with the exception of the final drive ratio for transaxles, and I assume the NSX transaxle has a built-in final drive ratio (i.e. the differential in a RWD car). Also check your auto tranny fluid level (with engine running) and look for any signs of leakage underneath. Low fluid could mean loss of line pressure especially during spirited driving (turning) and thus flared shifts from clutches slipping and could cause further damage all around.
Anyway - throwing out an opinion here - it's a good bet that the detuned auto tranny NSX engine is mostly or solely due to speed's effects on energy and transmission capability. If 8000 rpm is the manual redline and 7000 is the AT's, and since HP is essentially torque x speed, then ratioing redlines tells a story:
7000/8000 * 290 hp = 254 hp
In other words, it's not necessarily true that 250-250 hp is the do-all end-all value selected for optimum the transmission capacity or longevity. Possibly 254 hp is just the result of lowering the max engine speed because of transmission limitations. An automatic transmission is full of a wide array of mechanical rotating parts - planetary gears, needle bearings, one way clutches, spinning clutches, etc. You can "balance" the design of a rotating system like this only so much - generally, bigger parts are stronger and live longer but the bigger it is and the faster you rotate it, the more the forces. So in an auto tranny, a major challenge is the balance of durability (somewhat related to size & weight) vs. cost, packaging, fuel efficiency (for which usually size & weight are bad things), etc. Forces on rotating parts increase by the square of the rotating speed, so something spinning at 8000 rpm vs 7000 rpm is spinning "just" 14% more but the forces are 31% more, which is huge. Also, planetary gearsets work much differently than parallel shaft manuals and have various parts that sometimes spin several times faster than the transmission input shaft. We'd create component speed charts for each auto tranny showing the speeds of all rotating parts in each gear. 8000 to 9000 RPM doesn't seem like a big difference but something spinning 2 or 3 times that sees a big difference.
Another speed consideration is energy put into the clutches - the higher speed you shift under power, the more energy (heat) the clutches must absorb. Think about sliding on a carpet and rug burns - a little faster and a little too often equals lots of pain. That's a main reason why tracking an A/T is a bad idea - all that high speed frequent shifting puts a lot of heat into the clutches and then the tranny fluid, decreasing the tranny fluid life and its ability to function. Transmission fluid is amazing that it acts as the cooling fluid, while providing predictable & repeatable sticky friction behavior for clutch-to-clutch and band-to-steel actuation, while remaining slippery enough to lubricate gears, bearings, shafts, seals, etc., while being the medium to keep the transmission clean by transporting worn friction & steel material but while remaining clean enough to do all this consistently and with longevity, and when operating over a wide temperature range. Crazy!
I agree with the thought of some that the engines may have been tuned differently to play better with an automatic trans. Too peaky of an engine map/curve or ones that change shape drastically over various throttle positions make it difficult to smoothly calibrate an auto trans I believe, but that's a little outside of my experience to comment much on.
A couple other thoughts too regarding Honda's balancing act behind why the "weak" tranny and detuned engine - in general for the auto industry, rarely are automatic transmissions designed and optimized solely for one application. So they have to be flexible: weight conscious for fuel economy for lower-power applications, while being strong enough for higher-power applications, and not costing a lot to customize for the extremes. Like Ken/NSXTASY mentioned, it can sometimes make only so much business sense to develop a fully capable auto trans for a low percentage of slushbox buyers for an already low volume vehicle. But with the NSX being so focused on function, and with it being a clean sheet design, then it's hard to imagine any detuning not being the result of pure physics alone. I'm GUESSING the NSX transaxle was specifically designed for the NSX but because of the transverse engine, they didn't have the ability to package a long, larger and robust transmission behind the engine and down the length of the car center. I can't find much online but I'm guessing the NSX transaxle is a pretty compact piece of kit given the available packaging and the car's focus on low weight, compact size, etc., and was therefore very size and strength limited. There are a LOT of parts to fit into an automatic transmission.
Getting back to modding the engine beyond 252 hp and what the auto trans should be capable of - ignoring any modding talk for a second: just rating a transmission as having a meaningful torque capacity "number" is nearly impossible. A transmission does too much to be able to rate it for a certain power, torque, or speed. The easiest thing possibly would be to rate the trans for speed capability, but you'd have to rate it by gear - some gears could theoretically spin faster than others because different things are spinning in different gears; you'd just need to find the limiting component. But even THAT is difficult because sometimes a particular component's speed capacity is dependent upon lubrication availability and line pressure, and the pump & hydraulic system acts differently at different speeds depending upon various design trade-offs...and each gear could have a different speed capacity...you get the idea. Or you can rate it for max stall input torque (brake pedal down, accelerator down, engine screaming like crazy but transmission zero rotating speed, torque converter at max torque multiplication and making all kinds of heat), which just stating the torque that the transmission can hold when not spinning and is a function of line pressure, clutch sizes, clutch material, torque converter type, and gear/shaft/case strength in 1st gear. Or you could rate a trans for its ability to work behind a particular engine and then after balancing the power input, engine speeds, torque converter selection, etc., you could assign a general torque rating to the trans, but it really wouldn't paint the full picture. The problem with assigning a "number" or capacity to an auto tranny for something as simple as marketing purposes, or for trying to smartly rationalize power upgrades, is that the transmission does too many different things and is a huge balancing act. At the end of the day, we'd all design our individual components to meet certain bounding expected speed, torque, lubrication, temperature, etc. design inputs, but the ONLY way to verify the box's capability was to perform lots of durability tests. First on the test bench by component, then in a dyno, then in the various prototype vehicles. Excruciatingly annoyingly, sometimes a given trans would behave extremely differently in a minivan vs. in a passenger car, or in passenger car A vs. passenger car B, because of all the various different system interactions, engine characteristics (torque curve, speed ranges), vehicle weight, vehicle cooling system capability, etc. No doubt you could probably add a lot more torque into the NSX auto tranny if your main goal was straight line speed, let's say. But perhaps that'd be a hugely risky proposition if you planned to race and exercise those clutches for hours.
Anyway - I was surprised to see so many recent auto tranny posts and all the talk of transmission capacity and trying to justify what the transmission could do brought back some good memories. I was listening to click & clack during breakfast and just kept typing. No doubt the NSX auto trans powertrain could probably take a little more but good luck how to implement that "little more" in a way that will last a long time.
Had to turn on the pkg lights to see it ... . 
