I think you have been looking at the SGDAH drives (Sigma II series). The ones I've got are the older Sigma I, which can only do analogue speed or torque control.
I am just using an adjustable +/-10 V source for control, just trying to get a feel for the torque control mode. I'm building a servo controller which will be controlling these (
http://www.cnczone.com/forums/showthread.php?t=7785), so I wanted to get a hands-on feel of the torque control mode. It works about as expected, except what I described above.
Also, when set to speed control mode, the motors behave as expected (maybe a bit too much speed fluctuations than I like due to the cogging, but this may be because I haven't found the correct PI parameters in this mode).
Arvid