Hi Christian
I have an Audya 5 as well as a KN7000 and a G70. I haven't had a Yamaha in years, so I can't compare that except for demo's.

Soundwise, the Audya blows them all away IMO. The live sound is just what I was looking for. The OS to me is intuitive and have had little trouble learning the basics, at least.

I am not so impressed with the Vocaliser. It is in the middle of the pack, I would say. I have to have the best so I ordered the TC Helicon Voice Live Touch.

As far as accessability is conscerned, I don't consider myself qualified to advise you. I have, however, tried to put myself in your situation, and guess the following:

The Audya Voice List is a favorites list you can make up by category under each button. For example you can build a list of your favorite piano's under the piano button, or can put all of your favorites under any button, with two pages of ten slots. Once you had your instruments loaded, it would be a snap for you learn the right button, rather than having to scroll. You alluded to this and I think you are right.

In general, it is button driven, as you said, and would seem to be a better fit than most.

To be honest, I don't know how you manage as well as you do, given the fact that none of them seem to go out of their way to make them more accessable to the visually impaired.

I hope I have helped a little.
Bernie