Hi yes9310,
Sorry for the delay in answering the question. I wanted to look at the code again to remind myself what was up with the through zero option. As it is currently set up, if you run mono input, the left channel should be positive through 0 while the right channel should give you a negative through 0. This is just a cheap way of stereoizing the signal and giving you both options, but I realize it's not ideal for use if you just want negative through 0.
I'll add the negative through 0 and univibe to the feature request list and I'll see if we can get these in a future release. In the meantime can you try using your MF on the through 0 setting using the channel 1 input and the channel 2 output and let me know if that's the sound you're looking for?
Thanks,
Dan