Just read the blog post. 29% cpu resource for 4 XM channels is pretty amazing since Air Zonk does everything it does with 21% wasted on audio. I'm guessing that 6 channels would be fine running with most sections of an RPG.
Airzonk is a lot higher than 21% cpu resource. Just to be sure, before posting this reply, I took 10 readings from the game's TIMER interrupt. The actual cpu resource floats between 29% and 33%.
It was at 33% when it had to reload the bit shifter (decompress the samples), which if I recall is every three samples or so. It was about 30% for just playing the sample. That doesn't include
any music engine stuff (reading the byte code music for the normal channels). I made sure the samples (sampling of the code) I read didn't touch that part (that would give a false reading). So 30% just for playing the samples, and whatever cpu resource for regular channels.
For an RPG, I think you could get away with almost 70% cpu resource dedicated for audio (if the game is coded in assembly). That would allow much higher rate sampled channels.