Before we go further, please clarify what you mean by "disable zone switch."
Right-click any of your zones, bring up the Zone Switch configuration, and disable it so that it does not route any of your files to another zone.
That is correct. Source number of channels has never worked with multi-channel sources.
The only thing you should be doing is:
1) Play a
5.1 (6-channel) file in your desired zone.
2) Stop playback, open DSP Studio, and change the output from "5.1 channels" to "source number of channels".
3) Hit the play button again.
The output being sent to your device should not be changing at all.
If that still isn't working, please upload a screenshot showing the Audio Path when a 5.1 track is playing.
I can't think of a reason why a zone would be able to play 5.1 tracks when DSP Studio has the Output Format set to "5.1 channels", but cannot play those same 5.1 tracks when it is set to "Source Number of Channels".
JR is in fact mapping the channels, but doing so incorrectly under certain circumstances, as with the file Channels tag value on Mch SACD = variably 5 or 6, which is being used in Source Number of Channels.
When you select "source number of channels" you are telling Media Center not to do any channel mapping. It passes that task on to the playback device.
If you send that to a 'dumb' device like a DAC, the channel mapping will be wrong because a DAC typically will not do any remapping. Media Center isn't getting the channel mapping wrong, the playback device is.
When playing to a device like a DAC you
need to specify the output format in DSP Studio so that Media Center does the channel mapping instead.
This is why I think that Hendrik's suggestion to add a checkbox that outputs stereo files as a 2.0 signal may be the best solution.
That way you can have Media Center remap multichannel formats, but pass through stereo formats, rather than having to pass through everything to the playback device.