Thou I've not used the CSMIO/P-M but will shortly have it's bigger brother CSMIO/IP-S I can tell you the ESS is more than good enough for steppers and will easily do what you want.

The CSMIO is a cracking bit of kit and very high quality but the -M version doesn't allow slaved motors I believe.? So if your wanting this then the ESS will be better.

If you go with ESS then buy the PMDX 126 BOB Because the ESS can be directly plugged into it and with another daughter board the Gecko's can be combined making a very neat setup. Not cheap but high quality and the BOB is about the best in the business at this price range.

Just a note regards the frequency and ESS 4mhz max, The G203V have a maximum of input of 250khz so this is a limiting factor and in reality then you won't actually run any where near this. You'll mostly find your running a maximum of 100khz sot he 125Khz isn't limiting with steppers.

Servo's with high resolution encoders then it's different and you'll need the extra frequency. This is one of the reasons amongst others why I'm getting the CSMIO-IP-S.