I bought a 640p because of reviews and the fact than it has a rumble filter, and I love it. The 640p is "lifted" by the Pangea P100 power supply (killer design built like a tank) which recently got cheaper...$69 at "advisor", although I bought 2 of these for 100 clams each and thought THAT was a steal (use one for my DacMagic). Highly recommended. Plus, the 640p should be a deal currently since they've been replaced by the 651p which, according to "advisor", will accept the Pangea P100 cable size...THAT combo might sound better still, and remains relatively inexpensive.