I just recently bought a 04 V70R (premium sound 803 HU) and plan to upgrade the stereo, I have a few questions please.

-If I change to an aftermarket deck do I need to get the software reprogrammed by the dealer? I heard both answerson here. Also, any easy solution on powering the center channel as most decks are 4 channels only as well as steering wheel controls.

-If I leave the factor deck alone, I plan to run two amps, a 4 channel for the door speakers and a mono amp for a sub. Can I make RCAs out of the wires going to the factory amp and use the existing speaker wires for outputs from where the factory amp was? Basically just swap out the factory amp for an aftermarket one. Then use the 4 channel amps preout to go into the mono amp. If so, does anybody have a wiring diagram?