There is a trick to getting the USB audio to work, I'm not sure if this is the problem that you're experiencing but it's worth a shot.
From the H9000 FAQ:
When switching to a new sample rate, you should first change the H9000’s sample rate, then change the computer’s sample rate. The audio will be muted if the sample rates don’t match. If you switch the computer’s sample rate first (e.g. by loading a session with a different sample rate), you will have to change the H9000’s sample rate, then change the computer’s sample rate again once the H9000’s clock is locked to the new rate.
