Hello Reg
Regarding Wersi OAS instruments, I regret to inform you that screen readers do not work as it is a totally separate program, which for stability uses as little as possible of the Windows XP operating system.
The screen size and the buttons on the screen are of quite a large size, and possibly cardboard templates could be made.
Every function can be stored in a preset, so if you had assistance setting the instrument up, it could be operated in that manner. (You can select voices and styles without the touch screen, but is does limit the amount you have direct access to)
The number of presets available is unlimited; however by default it is set at 2500, but can be altered. (Professionals tend to have it set at about 8000)
The UK contact is Harmony Music of Boston. http://www.harmony-music.co.uk/index.htm
01205 355366
Hope this helps

Bill