Bitstreaming bypasses DSP Studio with, as far as I know, no way to do multichannel DSD to stereo DSD without doing a conversion (which is always going to be a lossy conversion).
So, the only workarounds I can think of right this moment are;
1) Avoid trying to play multichannel DSD files and stick with stereo. Probably the easiest, most straightforward solution.
2) Turn off bitstreaming and let MC do a on-the-fly DSD to PCM conversion with DSP Studio > Output Format > Channels set to 2 Channels (stereo), which is a lossy conversion, of course.
3) Turn off bitstreaming and use DSP Studio > Output Format > Channels set to 2 Channels (stereo) and DSP Studio > Output Format > Output Encoding set to whatever DSD setting you desire. This is also a lossy conversion step with a PCM conversion in the middle (so DSD > PCM > DSD).
You can probably create a new zone (with bitstreaming disabled on it) and use the ZoneSwitch feature with a rule for DSD files with channels greater than 2 to perform the second or third options automatically.