[ChrisZang]

I have a CDR-220 so I can only tell you how it works on my car:

WIth the CDR-220 I plugged the rear speakers directly into the radio and fed the two pairs of front speakers through the 4x40W amp.
Then later I also bought a 6x40W amp on eBay and now run all 6 speakers through the amp.
Difference in sound: ABSOLUTELY ZERO - waste of money!!!!
To answer you questions
a) It's almost plug & play (you need an additional harness which PNP sells, but it seems you bought it already)
b) The CDR-220 has an AUX-In for which you can buy an adapter from Becker, you then can connect your MP3 player or Satellite radio through the Aux-In (provided you don't have a CD changer)

Again, all above is for the CDR-220

Cheers