You suffer from the same problem I do, the dreaded 1991 Bose amplified speaker problem. I've found several places locally that will rebuild the speaker amps for around $100-125 each. Problem is that this will happean AGAIN in 5-7 years. I've contacted Acura Customer Relations as well as Bose Q/A but they both kindly tell you to get out your check book. There are NO real alternatives short of ripping out all and re-doing the entire sound system.
Good Luck. (Your local Acura dealer should know of an electronics repair shop that could rebuild your speaker/amps).