Where is stock amp in 05' 325....if i have one? And if i dont.....where should i hook up RCA convertor to, for amp and subs.....?

The stock amp is located behind the trim in the left side of the trunk. If you want to hook up an line convertor, you will either have to get a balanced line convertor and get it from the headunit input at the stock amp, or you could just use a regular line convertor on the speaker outs from teh stock amp, although the signal wouldn't be as clean.

I have an 05 325, convert, non HK. I pulled out the trunk liner and did not find anything there. I've been searching for an upgrade, unsuccessfully. BSW will sell me a sub upgrade and speaker upgrade but the sub upgrade seems a little excessive for my taste. I may do that anyway. Also their speaker upgrade shows a coaxial for the rear speakers. I see a seperate 5-6" speaker and a seperate tweeter. I think most people suggest no rear speakers are needed. I cannot find much information on how to upgrade my bmw. I would like to upgrade the amp, if there is one? Add amp & sub keeping the BMW h/u. Trying to keep it looking as stock as possible.