Perhaps there's a workaround:

Currently I have a mono speaker feeding from a mono output, which is great in that Totalmix auto sums to that output. But I'd love to have it set as speaker B - but if I do that, it has to be a stereo output and thus I lose the mono summing capability.

Is there a good elegant workaround, or could this be a feature request - to make the assigns not be limited to stereo pairs only?

Thanks!