Alero Questions?!

I have a 04 Oldsmobile Alero that I put a stereo in a few years ago. I have had quite a few different sub/amp set ups in it and it doesn't seem to get as loud as it should be. I was wondering if anyone knows anything about this issue like if there is something with these cars that limits the power output or anything like that?

Also I am having very poor radio reception with an aftermarket head unit, I assume it is due to having the antenna built into the back window but im not sure. I have tried 2 different antenna adapters but I am wondering if there is something I could get that actually works to amplify the antenna signal??

Any advice would be greatly appreciated!
Thanks:uhoh:

Please describe what's in the Alero, stereo wise

The car/radio/antenna is an engineered system, you will never get the reception the factory radio had because the Delphi radios are actually really good units. An antenna amplifier will just amplify the noise too, they are typically pretty crappy - it's why you don't hear much about them anymore.

I have a kenwood head unit with the gm antenna adapter, alpine m850 amp and a pioneer premier 3000 watt sub. All I get on the radio is static, it use to work alot better even with the kenwood deck in there but recently it has gotten much worse?

Pull the headunit out and make sure the adapter is still plugged all the way in and not cracked/broken.

That amps is a mono, so I am assuming the other factory soeakers are running off the headunit power. Getting bass in a trunk car is tough, seems most people get the most bass by facing the box with the speaker facing the rear about about 1/2 to 2/3 of the way back. Try different distances and facing the sub every way you can think of to see which is loudest - it's more of trial and error than science. Also, what size power and ground wire do you have for the amp ?