I switched to the ALSA driver from the OSS driver for my Creative Sound Blaster Live! card long ago, but I'm still not used to how MIDI is done. I'll record the relevant commands this time, so I won't have to look them up yet again.
Lately, I've had to manually load the snd_seq kernel module.
Programs I wrote that look at /dev/midi00 should now look at /dev/snd/midiC0D0. The behaviour of this device file differs too: I had to change my code so that it could handle a read() call that returned less than the requested number of bytes.
To play MIDI files on my digital piano, I run pmidi -p 16:0 foo.mid.
To send MIDI events to fluidsynth from my digital piano, I run fluidsynth 2> /dev/null (to get rid of spurious warnings), load a soundfont, then run aconnect 16:0 128:0.