No DSP was used. I believe just line out. I can ask for more details. My installer was quite sure a DSP wasn't needed and I believe he was right. It sounds very clear and crisp at low and high volume. I paid $3000 parts, install, box build, tax and I was in a hurry so they got me in quick.
Bought an XLT with stock (non B&O) stereo. Visited my local shop for an upgrade. ;) One 10" sub in small box under the rear seat. Component driver and tweeter in the front and two-ways in the rear. Using one 1500W 5 channel amp. Highly recommend the upgrade! Unbelievable difference: clean...