A follow-up post so I can address the actual question...
I've never attempted audio-only with any Trek except TOS, and that was a matter of technological necessity. Any conclusions I might come to will be semi-educated guesses.
I could be a smartass and say TAS could be a purely audio thing, since the visuals weren't worth keeping one's eyes open in any case.
It's likely that the other Treks would mirror my experiences with TOS - some episodes would work pretty well and others would be useless as pure audio. Just to pin myself down, I'll say ENT seems like it would hold up in audio better than the others.