Start work on Single Voice implementation for DMX compatibility

[sneakernets]

DMX cuts the second voice of double voiced instruments when channel pressure is maxed out. Make sure that all double voices sound reasonably good with the second voice disabled.

Basically any double voices that use the extra channel to add more harmonics to the sound (but aren't 100% needed) need to be the second voice. It'd be embarrassing if the harmonics were the primary voice and the fundamentals are placed on the second voice.