I have a 94 z28 with the 3 speaker bose....
If i were to get a sub from a 95 that has the 5 speaker option (so that i could run the back two speakers) would it work easy? or does the WHOLE system need to be changed.

 

I couldn't tell you if it will work, but I have a sub if you want to buy one. My guess is that if you are good with wiring, you could figure it out.