Deflemask seems more suited for music creation than music conversion. There are several example music tracks that you can try out. Just open the 'DMF' file and save it as a 'VGM' file. That's where the Green Hill Zone track in the example comes from.
If you just want to play WAV files I know that SGDK already has some tools to do that. You are looking for PCM playback. Unfortunately, you will find the sound quality to be poor for music and the file sizes to be quite large. Great for sound effects, and perhaps good enough for some grungier sounding music.
If you just want to play other VGM from other games, you will just have to look around for files that will work, or use a different kind of player. The Road Rash tracks I included in the example are actually from this website: 'http://ocremix.org/chiptunes
' and they seem to play just fine, but are much much more compact than the files from project2612. I might have to compare some of the same tracks from both sites when I have time.
Now that I've hacked on this project for awhile I feel like I understand the Z80 assembler a bit better and may rewrite parts or all of this in assembler eventually. Still not sure if it will be adequate to play some of those dense VGM tracks. The Z80 runs at half the speed as the 68k and is 8bits instead of 16bits. Might be fun to try, however.
Mostly I wanted to do this to have a way to create new music and have it run in the background with the Z80, for that it seems adequate at this point.