I'm using the kn7000, and I have no complaints about the mono sound. Of course, where I sit, I hear the stereo signal through the 66 watt internal amp. That's a significant addition to the room sound.
The acoustic piano on the Tyros didn't light my fire at all, so comparisons to stereo/mono are wasted on my ears. From the posted demo's of the stereo/mono samples ... I agree, the Yamaha sounds pretty lame in mono. That's yamaha's fault.

I don't want to get in any shouting matches about this PAS. I only want to try and educate those who have no idea about just how cool this new approach can be. It's a different concept. A different sound, and IMO a very large improvement over what we were used to in the past.
ie:
Last night was pretty crowded for St Patty's Day (even though I was in an Italian Resteraunt)and some friends came in late and sat RIGHT in front of the tower. I mean, RIGHT IN FRONT. Maybe 3 feet direct dead center of it. I watched their body language all night and listened to their conversations ....... there were NO harsh, peircing tones making them lean in to hear each other. There was no "loud spot" in front of the perfomance area, and the entire room still had an excellent coverage. There were people dancing in the back room even.

Short conclusion:
This has been said before, but is worth saying again:
If the signal you put INTO the Bose is excellent, then the signal you hear OUT of the Bose will be excellent. If your kb sounds like crap in mono ... it will sound like crap, only louder in the PAS.
It's a "garbage in-garbage out" theory that is being proven again, and again.

Don't fault the system for inadequate sound. If you put somethig wonderful in to it .... you'll get something wonderful out of it.

OK, I guess the rest is up to you to try for yourself. I won't try to sway your opinions. Gary Diamond is going to audition my setup tonight. He's a writer and maybe he can give you another unbiased opinion.