Following up - Support looked into this and believe that the chip that decodes the USB input is not capable of better than the rebook standard of 16bit/44.1Khz.

HOWEVER

Because I've got a Macbook Pro, I have a hidden TOSLINK output in my headphone output. Bless you Steve Jobs! As a result I can run the TOSLINK directly from the MacBook Pro Headphone jack to one of the optical inputs. When I did that the MIDI setup in OSX Lion recognized it and configured it as 24bit 96K.

Yay!