Using a great Stereo instrument like a Tyros, S950, Pa3x,Audya, Bk9, etc, and then condensing it's stereo sound spread in which it was created for into mono is defeating the purpose altogether & you are losing alot sound wise. There is a BIG Difference in sound & if you don't hear it, I wont say anymore on this subject.
But you do realize what YOU hear on stage and what your audience hears aren't necessarily the same thing don't you? I am guessing you have never been able to go to the back of the room while you are performing to hear how much stereo separation you are actually getting back there. I am not criticizing your desire for stereo imaging but just suggesting there is no way you can realistically judge the effect further back in the room. Though I guess making a stereo recording further back in the room would give you a good indication.