Sound quality appear better than from the OEM headunit but you have to remember that you're still going thru the stock amp and speakers. I guess anything is better than the stock radio....
Everything including volume is controlled thru the ipod.
All it consist of is a small electronic switch box that connects to the back of the radio (uses stock connectors) and powers the amp when the stock radio is turned off and and external switch is activated.
I don't know if you can still find these, it was a mercedes SLK R170 aftermarket accessory that I got from a guy that was going to offer them for the XF but not too many ppl showed interest at the time....They was a thread on here about it about 4 to 5 years ago.