Listening continues... both Roon and MPD sound pretty nice.
I think I've finished my listening impressions and it's a victory for MPD. There is just more impact/weight/texture to the music with MPD; Roon, for whatever reason, sounds compressed/congested with headphone listening. It's not night-and-day, of course, but I find myself wanting to switch back to MPD when I am listening to something I am really enjoying with Roon.
That said, I am going to keep Roon and use it to explore new music, which where the Roon UI really excels; I can do that for hours on-end.
One last note on this:
when switching between Roon and MPD, I am noticing odd display behavior on my BDP-1 and have learned to power cycle when switching between services. For example, after switching, the second line of the display will often stay blank and not display the playing artist. And, after switching, sometimes the display will go blank and not come back on, at all, unless I press buttons on the front of the player (I have the display set to always on).
Otherwise, Roon playback is robust and works without any issues (after the latest Roon update). Nice work, Bryston!