Are you using the Adriane version of Knoppix for the visually impaired? Or are you relying on the plugin you mentioned in the "regular" Knoppix. If you haven't heard and felt the Adriane system, just type in 'adrianne' at the boot prompt...

Cheers!
Krishna
p.s. It would definitely require the sound to work! Perhaps you can dig up the details on the sound chip/board and let us know what is required. Compiz requires hardware acceleration capability from the graphics subsystem.