No sound from MusE or Jack

I can't get any sound out of MusE. When I run a MIDI file in MusE, it causes activity in qjackctl, and also on the sound output bar within MusE itself, but there is no sound. I can get sound out of other programs (such as Firefox). I've tried just about everything, including installing pulseaudio-module-jack, adding commands to load module-jack-sink and module-jack-source to /etc/pulse/default.pa, running `pacmd set-default-sink jack_out` (which seems to work, as long as I restart pulseaudio using `pulseaudio -k` and `pulseaudio -D` after starting jackd - but still no sound).

I had a configuration a while back to pipe MusE output into LinuxSampler, but I don't think this is active (although it's hard to tell from the qjackctl interface).