Xpantastic!

>>There are 2 processors in the Xpandr/Matrix-12.

There are 3 in the Matrix 12, because it has 2 voice boards + the main board.

>>If one of these fails and you need a replacement,- your only chance is to buy a Matrix-1000 used.

I don't remember if the 6809 in the Xpander/Matrix is the 6809 or 6809E (External clock).
These are commercially available and dirt cheap
http://tinyurl.com/4qr3ajv

Hitachi makes a pin & instruction compatible replacement for the 6809, which runs up to 4Mhz(I believe).

Imagine what new features the Xpander could have if it would use a faster processor. Sure, a lot of code would need to be re-written,
but there are people who like to do that.