@auxinput I fully agree, which is why I’ve been chasing this irritating fly in the ointment for so long. Moreover, the native file is how the artist released the material, and one would presume that’s how it was meant to be presented.
It also turns out I spoke a bit too soon about everything working correctly after my quick test. Hadn’t looked at the output data carefully enough. Turns out that while JRiver is now presenting the native frequency (44.1, 192, whatever), the bit depth is fixed at 32. This is confirmed by both the audio data window within Media Center 27 and the C50 on-board display. The data window shows the native data and the output data. The output data matches the C50 display. One example was a Linn classical piece with native 24 / 88.2 and was running at 32 / 88.2. It sounded quite a bit better than when both bitrate and frequency were upsampled, but still artificial.
I’ve posted on the Media Center support forum to see if I’ve missed setting a software switch somewhere; no replies yet. The Apple support forums aren’t especially helpful other than to say that the MIDI interface will only output at whatever bitrate and frequency combination is selected in it. I knew that already and am trying to bypass it as @sandstone suggested. This whole computer audio thing is very frustrating. All I want to do is play digital music in native format. The only device I have that will do that is my MVP-881BR. So far, it’s the hands-down winner in both convenience and sound quality.