I worked out a solution. I switched Aux mixes 1-4 from mono to stereo. Only assigned one side of each Aux to an XLR output. Assigned Aux1-left chan, Aux2-right chan, Aux3-left chan, Aux4-right chan, to XLRs that go to the 4 mono stage monitors. Then, when assigning stereo inputs to these stereo Auxs, set the balance left for Aux1, right for Aux2, left for Aux3, right for Aux4.
So now we have our standard 4 independent mono monitor mixes for normal band operation, but with stereo effects, and stereo pre-programed music listening. Oh that wide open feeling.