In muse 2.0rc2 my midi controller keyboard showed up in the "midi configurations" window in any of the "device name" drop-down menus. Since installing muse 2.0 it no longer shows up.
as I wrote in the forum this was a late change we made to MusE.
The idea was to focus more on the jack enabling features.
For future reference, the way to get it working is to either start Jack with -X seq (so jack sees the alsa devices)
or start MusE with -A so MusE shows the alsa devices.