Hi iaresee
the way you want to use MF has really nothing to do with it being tru stereo. A stereo FX is something completely different from a dual mono configuration you are asking for. The other problem is that using the same unit on two different electical impedance circuits is definitely not adviced. A pre_amp position requires -10dB and an FX loop insertion a +4dB impedance. So the answer is no, you can't use MF in such way. Only the rack units can do this.
best
I
