As far as the DAC switching is concerned , yes , so long as the command is correctly interpreted, if a .dsf album is followed by another .dsf album or If the same album is replayed there would not be any switching.
Unfortunately the fact that the issue’s appearance is intermittent makes it difficult to trace the cause. I have now run out of what I had hoped might provide straightforward answers. Obviously I cannot try to replicate the issue here as I do not have a Bartok. However I think that we can eliminate the UPnP server from the suspects’ list as it seems that the issue occurs whether MinimServer is used or Asset. I suppose there could be the odd and unlikely chance that they both exhibit the same oddity though.
So it is back to Mosaic control and Bartok and/or what connects them, the LAN. As I say I have run out of ideas.