The ESS is a much nicer product than the SS, I still think the SS was good and I never really had any of the issues others seemed to have. One thing that still bugs me about the ESS is the step/dir spindle control still has its glitches and I waited a long time for it to be sorted but unfortunately it never was. It may get done at some point but when I have no idea.
Regarding the CSMIO, yes it is more expensive but when you look at what you get it starts to look cheaper. Firstly everything is integrated into nice din rail mountable boxes. You have the spindle control built in, the Analogue inputs built in, plenty I/O with expansion capability, differential Step/Dir etc etc. When you start to add up a ESS, a dual port breakout, spindle controller (if analogue spindle) means of getting analogue ins for FRO etc, line drivers, conversion boards for 24v I/O then it doesnt seem to be quite as expensive in my view. Also there seem to be more possibilities, rigid tapping I think will be one of them, already the encoder module for threading takes the spindle encoder in and even altering the spindle override whist threading the axis seems to track it very well. I have just got the wee lathes axis wired today and I managed to do a test for threading whilst altering the Spindle Override and it looked good, still a few potential hurdles to overcome but things seem to be progressing, Heres a vid of the wee lathe tested today.
http://www.youtube.com/watch?v=HC1PK6uD26UHood