The problem with that, is that it sends files to their own playlists and if you play a track in another format while one is currently playing, it will error out.
Unless you actually need to output the matching number of channels, I don't see much reason not to output everything in the highest number of channels that your device supports.
Possibly, you are right, but I have not encountered an error. But, yes, the playlists are separate for each zone. I just don't use playlists that often myself. As a classical listener, I just tend to select one work, usually with multiple movements, from one album at a time, stopping play before going on to the next.
Yes, I want the playback to match the input channels, but always with JR bass management applied for X.1 output. I do not want everything synthesized to 7.1 from 3.0, 4.0, 5.0 and 5.1. With the SACDs in my library, 3.0 and 4.0 appear as 5.0, but with null channels. Stereo is, of course, no problem by checking the box to make 2.0 input into 2.1.