Over the years, I've been in many NSXs with aftermarket exhausts. The one that has the least (if any) amount of drone are the bespoked ones that use Magnaflow mufflers.
This is the very reason why I went with Magnaflow for my GTO and NSX.
Magnaflow are the only ones that I have found to be packed with Italian RockWool.
It is sourced originally from lava deposits found in volcanic rocks which are melted in a cupola furnace (sort of a man-made volcano). The lava rocks, taken right from volcanic areas that have experienced recent eruptions, are dumped into the giant furnace which heats to a couple thousand degrees. When the re-melted lava comes out of the furnace, it is spun, sort of like cotton candy and a special chemical treatment is added to give it water-repellent characteristics, then the whole spun material is bound together in a wool-like fleece, which is ideal for use in high heat applications and acoustic control.
What better to deal with the high heat of exhaust, the volcanic ash?
You can only image the amount years of development it took to perfect this process, and get the process correct.
This process is actually extremely expensive for them, much more expensive then if they were to use the same material that every other company uses. But this also ensures that over time, you will not loose that Magnaflow sound!!