Check out Henni's many posts about the Audya, and Ketron's own website (
http://www.ketron.it/index.php?option=co...28&lang=eng ). The Audya sounds amazingly real for the most part, and if the internal ROM styles work for you, if you can afford it, it is a great arranger! If you can't afford it, you can't afford the Tyros either, mind you!
It will take Yamaha about 100 more years to catch up with Ketron at the baby steps pace they are on now. If you like the idea of loop based arrangers, forget Yamaha. They are only now dipping their toes in waters Ketron swam in well over ten years ago. Currently, Yamaha does ONLY drums and percussion on audio, whereas the Audya does drums, perc, bass, guitar and some other parts in audio too... Lord knows if Yamaha will ever go that route. And only 10% of the ROM styles are audio drums on the Yamaha, and new styles have been few and far between so far for the S950 (which introduced this feature to Yamaha's) and impossible to load in quickly.
If you like the idea of loops, currently, the Ketron is the only real way to go...