I must say that Honda forgot when designing the car that a sound system is just as important as HP! I replaced my whole system with Phoenix Gold speakers in the doors and trunk. Using space adapters you can put bigger speakers in the doors. I think I went 6", and for the rear remove the starform insert in the trunk and get a custom box made to fit flush with the rest of the trunk floor. It will easily take a 10" sub. As for the amp single channel will do. I kept the original head unit if you remove you lose the ability to use your external controls..Sounds Great!
Good Luck

 

One more thing you don't have to use a 4 channel amp to much for a small car. A amp is just need to drive the sub in the trunk I tried all the different combinations. Trust me you need a sub for this system to sound any good...Vin

 

You're budget's way beyond what I was willing to spend, given my 3" exhaust and loud mufflers, but I can put in a strong vote for Lucid (they do great work and offer great advice) and for rear speakers (they make a HUGE difference). Good luck.