It is a bit counter intuitive but you need to set the sample rate on the computer after you set it on the H9000.  If you get the mismatch warning, change the sample rate on the computer to 48 and then back to 44.1 again.  You shouldn't need to restart the H9000.

This is a consequence of the H9000 using asynchronous USB audio.  Unfortunately there is no way for the H9000 to force the computer's clock to re-sync when its sample rate changes.  The computer has to initiate this process.