Stock Speakers in 2000 Pontiac Firebird, Need Advice and Info

[MCS]

I had my two backseat speakers replaced but to my surprise the new speakers sound worse then the stock that were blown out. First I'd like to know, are the backseat speakers 6 1/2 or 6 1/2 x 9. Second where can I find information on the stereo system regarding all speakers sizes in the vehicle. Also it was brought to my attention that if you put after market speakers in they won't function right unless an amp is installed. I need to replace the back two speakers since one blew out so any advice on my car stereo system set up would be appreciated.

THANKS

[Sas]

In my old TA, when I put aftermarket speakers in, I just bridged the amp wires to connect the aftermarkets and they sounded just fine. If I remember right they should be 6 1/2's in the back panels.