Thanks for taking the time to type that out, and this is one of the things I'm worried about with this particular car. I wish I could upgrade the head unit to something I'm used to, but in this situation it controls everything from the seats to the key fobs. This car has the 15 speaker BOSE sound package, and supposedly it's active, the front stage sounds amazing. It has a 10" sub in the rear deck that in my mind I can take the sub out, replace with an 8ohm, 50w resister and use that input for the line converter, while still keeping the active control of the OEM amplifier happy?
Maybe it still makes sense to use some kind of processing hardware? I don't want to do this half ****ed.