I'm sorry, at first I thought your question was about the Qb in particular, and I didn't notice that you're using the Mac version of MC. I'm using the Windows version, so my experience may not apply. But here goes:
Tools | Options
Select Media Network, then "Add or configure DNLA servers"
Click Add and then select "Audiophile 24-bit DAC"
Change the Audio mode to Specified output format
Format: PCM 24-bit
Click Advanced, then select DSP Studio
Make sure Output Format on the left is checked, then change the Output column to 44,100 Hz or 48,000 Hz for each input, as appropriate
After submitting/closing, find your Mu-so Qb in the Playing Now tree on the left
Right-click and select Associate with DLNA server, then select the Audiophile 24-bit DAC
You should probably restart Media Center at that point. If that doesn't help then I apologize for jumping in on a Mac topic with advice from the Windows product.