oops! your right, I did see the 'brushless' part and didnt notice they are all AC motors
if you search yahoo for "servo motor amplifiers" you will get lots of websites showing up, and there should be some that explain how they work better than I can do off the top of my head.
these guys might be closer to what you want:
http://www.copleycontrols.com/motion...iers/dc_b_amp/