I sold my S750 ages ago (two years ago i think) but before this, i did order
a cable from redmond-cables. Unfortunately, some hickup did occur and the
cable i got in the end did not work. I had an old Atari colour monitor
(1084??).
I did solve it anyway by building my own cable, using parts from a company
called "Elfa" here in Sweden (similar to Radio Shack i would suppose). I
don't remember the details anymore, but i did get hold of a Roland service
tech who provided me with the blueprints for this cable. I remember having
to use a couple of resistors and twist a couple of the connectors to get it
to work (while fiddling with this, i got strange result with a garbled
picture, etc). It finally came out ok, but it was a little bit of work to
get there.
Perhaps this can be a little helpful for you?
Kind regards
Daniel