blaupunkt tha series amps

Does anyone have experience with these new amps.I have an 07 Milan with the 8 speaker Audiophile system that has a small amplifier for the 2 6x8 woofers in the rear deck.I want to replace all the factory speakers,have the front doors on channels 1 and 2,have the rear doors and new deck speakers on channels 3 and 4,and leave channel 5 empty for a sub in the future add an amp.According to Crutchfield,i could purchase either the 4 channel Blaupunkt THA475PnP or the 5 channel and use the matching Blaupunkt direct harnesses and be done.My thing is these new amps with the harness are designed to use all the factory wiring so that you don't have to run any new wiring.How much better would the sound be not only with the new speakers and amp,but using the oem wiring?"ole blake"