While stereo is always nice I don't think anyone other than the performer and a small percentage of the audience in close proximity to the stereo field really get the benefit of it. In a large room those further back from the front probably don't notice much difference. Especially with the Bose L1 which make a point of being a non-directional sound source. I have heard acts using a single L1 system and the sound has still been great. While using 2 L1s would be nice I don't think it's critical to getting a great sound.

My rock cover band used 2 L1 systems for a while. While they were great for the vocal spread in the room even 2 didn't provide enough midrange to reinforce a live amplified rock band. We ended up returning to a conventional PA system. But I think either 1 or 2 L1 towers work perfectly for an OMB situation. After all the Bose L1 was never created to be a PA system but may performers found it could do a great job in that capacity. Originally the L1 was called PAS ( Personal Audio System ) designed for each performer to have their own. Sure stereo may help overcome problems in mono summing .... but then the problem isn't the sound system but the keyboard engine sound design itself. Spending an extra $2000 seems like a non cost effective way of dealing with a keyboard design issue.

Now I think we are all done with L1 discussion on this thread. Start a new one if anyone wants to pursue it any further.