Srajan, over at 6moons, has found a SD card is the best way to listen since it leaves out the computer (with all it's noise), leaves out streaming (with all the various boxes, decrapifiers, cabling, etc.) and CD playback (spinning disks, vibrations and noise).
It hasn't a fancy UI that one can go ooooh and ahhhh over but it's a time proven technology that's pristine in it's playback. You can make lots of files of music on a postage stamp size format, separated out any which way you want but you have to settle for the low tech readout and it limits playback options. Not a big sacrifice to make for great sound, or so he says.
I don't see why USB playback would differ unless one can get a better device optimized for it instead of what comes with an all in one integrated (not to knock your integrated but on most like that, it's more a convenience).
All the best,
Nonoise