New Head unit

IIRC i didn't have to buy any special adaptor to make my factory amp/speakers work with my aftermarket radio. you simply buy one of the GM wiring harness kits and wire it up as normal. I'm on my 3rd stereo in my car wired this way with no problems. i just put a new radio in a month ago. i reused my wiring harness kit each time. i bought it at best buy back in 2004 right before i bought my car. you will need an antenna adaptor though as GM uses a different style than most aftermarket radios.

[ame]http://www.amazon.com/Metra-70-1858-Radio-Wiring-Harness/dp/B0002BEX8W/ref=sr_1_1?ie=UTF8&qid=1359512134&sr=8-1&keywords=1995+trans+am+stereo+wiring+harness[/ame]

I was told that you need the adapter in order to control the factory amps because the aftermarket head units don't work with them

all i know is all of my speakers work, including the speakers by the rear seats where the factory sub is, and i can hear my factory amp kick on when my stereo comes on. i actually had a situation with my last radio where it stopped working alltogether and i could still hear the factory amp kick on so i was pretty sure it wasn't the amp. it ended up being the volume control knob on the head unit that went bad. after playing with it for a while i ended up getting full volume sound or no sound at all, but it proved to me the amp still worked.

when you say control the factory amp what do you mean? the speakers are either amplified or they arent. if you mean like use an equalizer, my aftermarket stereo has a built in equalizer and i can change the sound types just fine.