1) I assume you are using windows? Which version?
2) when you unplug the usb cable from the computer and foobar plays the files, what is playing the sound? Or do you mean that Foobar just seems to play but you don't actually hear any sound?
3) can you play CD-sourced files (16/44.1) over the usb into the zodiac?
I don't use foobar or usb audio, but it sounds to me to possibly be a driver issue.
Does the zodiac appear as an audio device in windows?
Lastly, It seems no one on this board has an exact answer at this time, I'd suggest contacting the manufacturer for their opinion as I think USB audio over 96khz requires custom drivers on windows, and they may very well have had users with your problem before.
Let us know what happens.
Todd