HMM.....
Very brief look at the driver manual. Looks like you can bypass their board and go directly to the driver.
You can select 1/8 step for microstepping, the frequency rate may limit ipm, disable the current limiting function ( if automaticaly turns off during an idle time you may have problems) and they give you what you need in general, so that looks promising.
Now, how the other board is tied into the drivers ( ie; if cable that's rather easy, if via the board it's mounted on then you need to trace it all out PITA/ not impossible ) and i haven't the foggiest idea without looking at it.
You'll probably need to do some rewiring where the DB25 is connected to the first board.
STRONGLY, suggest you find someone that is familar with electronics to help you out as otherwise you can ruin what you have. Also before you attempt doing all this try and find out how the drivers preform after a modiication
as you may go through a lot of work and not be satisfied in the end.
FWIW, I have four drivers sitting here that realy need to be run by programing via dos, etc, and a rep was kind enough to say they were "old" technology, yes you could convert them , but their operation would be very unsatisfactory. I kind of got that feeling about you drivers, but then, i can be totaly wrong.
It's your stuff......LOL,
RICH