Len, If your PA does a good job why not disconnect the monitor speakers on the keyboard. then you would be able to turn the mic. volume up.
When I was using a Tyros 3 that was my setup. The Tyros 3 does not have speakers. There are some that use a small momitor speaker and not the onboard keyboard speakers, although that translates into carry more stuff.

I share the same feedback problem and sloved part of the problem by using a better mic.

John C.