Actually, I have SD5 and Yamaha PSRS900. I find the registration system on SD5 far superior to the Yamaha. I have a virtually unlimited number of registrations at my fingertips and I can quickly find and call them up, either by selecting from screen or entering a 3-digit number. Once you get it organized it is a very efficient way to work.
It's also quick and easy to save style changes or registrations on the fly.
The vocal harmonizer is excellent also and I love the Strat Guitar sound.
I can only imagine how great the Audya will be!
DonM