To go linuxCNC, you'd need something like the Mesa 5I20 ($199) and the 7I33 ($69) daughterboard, plus you'd proably want a 7I37 ($69) to get 24V tolerant inputs/outputs.
The only reason I know about the Mesa stuff is I did consider LinuxCNC, but other than some very basic details about cards that are compatible, I couldn't find any great details about how to set them up or what scripts would be needed to get them to work.

In the end I opted for a Dynomotion Kflop and Kanalog, as the support for both Mach and Kflop is far better.
There are other motion controllers that will work with +/-10V drives. Galil (pretty highend stuff with pricing accordingly), and CS-Lab (relatively new, but their stuff looks good although pricing is top end hobby/lowed end industrial) are two that spring to mind.
To use servos with Mach, you need something to close the loop outside the computer. As has been said, Mach only ouputs step/dir and isn't capable of closing the loop. You either need to close the loop in the drive (most modern servo drives are capable of this), or the motion controller (i.e. Kflop/Galil/CS-Lab CSMIO-A).

The PMDX126 is essentially just a parallel port break out board with a few extra features. It's certainly not capable of closing the loop for servos.