My main objective is to have a rear USB input deck. The Kenwoods have a good look, USB and a decent voltage preout. One of these decks use ACdrive which is just like my VW phatbox. I wonder if the other units have it, but just don't advertise? Please help me with the advantage to each deck. www.woofersetc.com is where I'm buying from. KDC-MP535U - Kenwood MP3/WMA/AAC/CD Receiver Item#: 76293 $164.99 $164.99 KDC-X591 - Kenwood Excelon USB/AAC/WMA/MP3/WAV/CD Receiver with External Media Control Item#: 76430 $169.99 $169.99 KDC-X590 - Kenwood Excelon MP3/WMA/CD Player Item#: 74933 $199.99 $199.99 DEH-P6900UB - Pioneer MP3/WMA/AAC/CD Receiver Item#: 76511 $219.99 $219.99 KDC-X791 - Kenwood Excelon USB/AAC/WMA/MP3/WAV/CD Receiver with External Media Control Item#: 76431 $229.99 $229.99 Thoughts on each?