Can I ask Why you want to change.?

I've used this setup and while they work very well the only reason I'd use them over standard stepper is because the motors are 3 phase motors which give much smoother operation and stronger thru out the rpm curve compared to 2 phase steppers. The actual Closed loop isn't that important or needed if normal steppers are sized and tuned correctly.

Normal 2 phase steppers matched to decent digital drives like leadshine DM, EM or AM drives give great performance and reliabilty for the money. You'll get DM556 and 2 or 3nm Motor for around half the cost of the C-loop and if run with around 44v they'll work great. If the gap was closer on price I'd say go C-loop for 3 phase motors but unfortunatly it's not.

Also if looking at the Larger C-loop motors then I'd look towards servos because most are just normal 2 phase steppers which offer no advantage other than the C-loop over normal steppers.