Are you happy with them? (do you get decent speeds before they stall)
I built my CNC using some old stepper from old dot matrix printers...they're doing the job, but the speeds are a little slow! Steppers will most likely be the first thing I upgrade & I had my eye on those Astrosyns myself.
Re drives...I pushed the boat out & rather than make one, I imported a drive from the States - it's one of these ....
http://www.easy-cnc.com/3axisdriver.html - I'm very happy with it (think it cost me about £85 delivered as he had a deal on Ebay at the time)