There's a comment on the manufacturer's page that says:
"Class compliancy supports 16-bit/48kHz 2 x 4 operation on OS X
10.3.9 and higher. Driver installation required to access more I/O."
Looking at Linux's USB audio driver, there are some quirks for other
M-Audio interfaces related to enabling different input
combinations. Perhaps yours needs something similar, but the driver
doesn't yet know about your card's USB ID?