That was people were doing back then, but there is nothing that keeps it from being driven by other controllers.It looks like the optos are driven directly from the LPT port, one for each channel.
Edit: It's a design by Bob Cooley around 2005 http://computerchristmas.com/ForumBoard/read.php?f=4&i=4486&t=4436&v=f
That was people were doing back then, but there is nothing that keeps it from being driven by other controllers.
Perhaps someday I'll find the "manual" and have some fun.