Does anyone know if both the stereo output jacks and the mono jack can be used simultaneously?  I'm trying to feed a stereo DI to the PA and also send the mono signal to a bridged power amp/one speaker cab.

It's OK to use all three outputs. If you use the mono with A or B (or A and B) there is a small amount of crosstalk. It's not horrible, but it is there.

That's ok.  In a live situation with the kind of stuff I play, it shouldn't be a big deal.  I will get to do an A/B comparison soon.  Thanks.