Ok. What we use at Biosero is a Peter Norberg Controller (BC2D20 to be precise). This thing can control up to 2 motors at a time, and another version will control up to 4. They will work for what you're doing, and they can be controlled from a PC and a micro.
If you're running things in a coordinated fashion (and based on your description), I don't see the necessity for real-time control, but rather good timing and response.
Arduino does have stepper motor boards. Not sure if they'll handle 8 steppers though. Might have to network and do timing? Or build your own?
Writing the Arduino code shouldn't be that difficult (high level procedural, and there's not too much junk code for getting set up). I have no idea what your control system looks like codewise, so can't really tell you which would be better.
As for which forums - your project seems to be a systems engineering project (controls with something that sounds oddly like somewhat complex mechanics?). I'm not surprised you can't find a forum - it's not a simple Q&A kind of question. For the controls questions, possibly go to the EE stack exchange forum (
http://electronics.stackexchange.com/), or the Programmers Stack Exchange (
http://programmers.stackexchange.com/).