I know there are some very knowledgeable audio folks on here and I hope you don't mind taking a second to read this as I have read nearly every article and post on here about adding subs/amps and swapping speakers 1-2 times and just wanted to clear up a few things. I have installed and used basic car audio components in a few other vehicles but am by no means an expert. From what I have read, this project seems very feasible.
My X5 is a 2001 with the business cd, a cd changer, no dsp, and a rear seat dvd system (installed by a previous owner). What I would like to do is add a 4 channel amp that fits into the rear passenger side compartment. Run two channels to new front components via the existing wiring, and bridge the other two channels to a subwoofer in the back.
Many of the posts on getting a preamp signal concern vehicles with DSP, but in my case is getting a signal as easy as tapping the lines from the HU to the rear amp with a LOC? I have heard conflicting stories on whether or not this signal needs EQing or ground-loop isolation as well.
For the record I want to try a set of phoenix gold rsd6cs two way components in the front as they get great reviews and I think the 6" woofer will fit well. I also want to mount the tweeter in the dash mid location for imaging. Trying to contact PG about what the x-over point is on this set. The amp would probably be something in the 4x100 range and I am undecided on the subs so far.
Thanks a million!!