When I was doing a lot of gigging, I panned both channels of the mixer to center. To my knowledge (and I could be wrong), when L and/or R are panned to center it is sending full signal from both the left and right channel to both XLR outputs.  This limits your stereo capability, however. We never ran our P.A. stereo, so stereo effects would have been lost as soon as it hit our mixer, anyway.I did try running both right and left XLR outs to the board, as well as Left only. They both worked, but I could never get a straight answer from our soundguy as to which was better.  With this setup, I set input 2 to same.  I'm not sure that you would need to do this and never tried anything different.

I also experimented with running everything in the HD in path A only. I muted the right channel and panned the left channel to center. For this to work properly,I believe you need to have a mono effect at the signal chain split. For this setup, I set input 2 to variax or aux.  This seemed to give me a cleaner (albeit weaker) signal to the board.

I would say that if you're running a stereo P.A., pan your HD mixer hard left and right and run a seperate XLR or 1/4" for each and pan accordingly at the mixer.

Hope this helps, man.

I'd go with 2 xlr's or the mono 1/4" or both 1/4" outs. If you use just one of the xlr's, your signal is going to be cut in half regarding volume, and yeah, it will mess up any stereo effects, as the xlr outs are intended to be used together in a pair, and not one or the other in isolation. I suppose if you ONLY use mono effects you could use just one of the xlr outs IF you need to cut your volume in half, but that would be an odd way to go about reducing your signal.