I had very poor performance using one Bose L1...Yamaha's stereo sampling doesn't collapse well to mono...the instruments are designed to work in stereo.

I used two Bose L1 systems in stereo...absolutely the best sound I've had with the Tyros and PSR.

Expensive? Yep. But you only have to buy a PA once, and with the Bose, you don't need a separate monitor system.

Ian