I just installed a Pioneer DEH-7400 head unit and 4 6993 speakers in my base RSX, and they sound great! I was considering installing the Bose system, but as stated many times in this forum, it is weak. Even with the factory sub in the spare tire, my system has just about as much bass.
Install of the head unit was a snap. With the base model RSX, the aftermarket unit mounts right in with no kit needed, just a wiring harness. Follow this link for an excellent step-by-step instruction

http://performance.clubrsx.com/headunit.html

Try to listen to a factory Bose setup in an RSX before commiting to buying one. The 6 disc/cassette/ cd all in one is neat, but an aftermarket will give better sound and upgrade flexibility.