Hey LeeZone,
The question about model differences especially with Yamaha is really open to opinion.
Yes, maybe a little different case, some different colored buttons, but to my ear , really not any substantial improvements in overall sound. I had a PSR 1000 and the differences between that and the Tyros 3 in sound quality wasn't much.
Personally, I like the 1000 better than the Tyros3.
The Tyros4 added some cool doo woop voices to many of their styles and maybe some slight improvements to some of their solo voices. Does a few changes mean it's a new model?
Yamaha could have accomplished the same thing with a software upgrade for the Tyros3. Instead you have to go spend another $4,000 to move up one number.
Don't get me wrong, Yamaha makes some really great arrangers.
I just like the fact that Ketron offers great new stuff for $60 instead of $4,999 again.
Yes, obviously Ketron has it's problems, but I think the Audya is worth the aggravation.
Now, Korg's Kronos, that's a new model, and a pretty exciting workstation from what I've seen and heard. Next year, I'll be adding one to my array.
In the meantime, when it FINALLY gets here, Ketron's upgrade will kick up the fun factor even higher.
Jim