Last night I used my Magellan 800 for a doubling gig, plugged my electric into the main input, and plugged my upright through a Grace Designs BiX preamp into the aux in. Jeff had recommended using the FX receiving jack, though that appeared to mute the Magellan's preamp circuit, so I went with the Aux in. It was a lower level through the Aux in, but I still had plenty of stage volume, and was also sending separate lines from the BiX and the Magellan. It seemed to work fine, though I might experiment some more. I really love the Magellan, and last night made me confidant it's a keeper!