I don't remember exactly what I did to cause this, but now I can't hear any music through the RM2K editor unless I have Windows Media Player open. I think I accidentally opened a MIDI file in WMP while one in RM2K was still playing. WMP doesn't need to be in play mode, it just literally has to be open and MIDI files will play through RM2K. This also seems to be affecting RM2K3, but not RMXP. There is no MIDI audio when I play RM2K/3 games from their respective executables, either. The easy reboot fix unfortunately was no help.

Can anyone offer any insight?

When you press PAUSE on WMP, it makes your synthesizer volume automatically go to ZERO. The effect? No midi music. Basically, don't pause your music on WMP, just play it and then close WMP, or stop the song, don't pause.

It works. Danke.