Only those? Damn, just knowing that I can sense that will give you some headache, so good luck with the workaround!
Though I think you could just use the voices as SFX, however that would not be that intuitive for the players who just want to mute the voices; oh well, I'm just a rookie who doesn't know anything, so take everything I say with a grain of salt.
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It's indexed at the end of the post; just scroll down and take it. Couldn't you just go back a few pages in the thread like everyone else?