I recently read that the Oberheim Matrix-6/6R supported remote control functionality. I did a quick search and came across
this page. I back tracked and found the site had sysex pages on a number of synths. Title link takes you to the list. As for remote control of the Matrix-6, check out the Matrix-6 page for the full list, however I noticed this interesting bit:
"Select Quick Patch Edit
This operation selects the Quick mode of the Patch Edit function on the
M-6.
The M-6 must be in Patch Edit mode in order to act upon parameter
change commands."
The Matrix-6, and 6R are notorious for not working well with external knob boxes. If you are having trouble getting one to work, you could try it in Edit mode. I think I did once and still didn't get my Matrix-6 to work, but I believe I have an old OS.