Found the review
http://www.enjoythemusic.com/magazine/equipment/0109/marantz_sa8003.htm
"The USB input is powered by an NEC uPD63901 microcontroller (designed for use in car audio head units), and it enables the SA8003 to play MP3, WAV, WMA and AAC files directly off a USB hard drive, pen drive, or iPod (it does not function as a USB DAC, as connecting a laptop to the Marantz with a USB cable does nothing). The uPD63901 does its own D/A conversion, so files read from the USB input completely bypass Marantz' CS4398-based digital section (and cannot be output via the Marantz digital outputs). The USB signal still benefits from going through the SA8003's discreet analog output stage, but overall the USB sound is not quite up to par with what the SA8003 does when playing a shiny disc. "
http://www.enjoythemusic.com/magazine/equipment/0109/marantz_sa8003.htm
"The USB input is powered by an NEC uPD63901 microcontroller (designed for use in car audio head units), and it enables the SA8003 to play MP3, WAV, WMA and AAC files directly off a USB hard drive, pen drive, or iPod (it does not function as a USB DAC, as connecting a laptop to the Marantz with a USB cable does nothing). The uPD63901 does its own D/A conversion, so files read from the USB input completely bypass Marantz' CS4398-based digital section (and cannot be output via the Marantz digital outputs). The USB signal still benefits from going through the SA8003's discreet analog output stage, but overall the USB sound is not quite up to par with what the SA8003 does when playing a shiny disc. "