I ALWAYS use two speakers. Arrangers were designed to be played back in stereo. The effects work as designed when you use two and pan them. Even if the audience doesn't hear stereo, and they probably won't, you will never convince me that one speaker with the channels summed sounds as good, particularly Yamaha arrangers, and particularly the piano. I know Gary edited and got a good workaround piano sound, but that shouldn't be necessary.
Besides that, I always have a backup in place and ready to go in the rare instances when one fails. And I had Bose speakers fail on three occasions.
So far the Maui 5s have been great and I only had a problem when I tripped over the power cable and loosened the connection. I easily made it through the night with the other speaker and repaired the connection the next day.
Worst case was when I was using ONE original Bose L1 and sub and blew the fuse. Had no spare fuse. (I still have several Bose fuses if anyone needs one! ). I had to call my wife to bring another P.A. system from the garage, so was without a p.a. for half an hour. Longest break I ever took and it will never happen again.
Now if you are doing a nursing home and half the people can't hear well anyway, sure one will work just fine and nobody will know the difference. Except me of course.
Deane, I just KNOW that Genos sounds better in stereo. You'll have to drive over here and play it for me to convince me otherwise!! Dinner's on me!