First thing is the G100, and Pixies are no longer made so that is not an option. The G100 never worked properly with Mach and the pixies sometimes worked and sometimes didnt, it depended on your amplifiers and as mentioned the guy stopped making them anyway.
There are a few options though.
If you wish to keep the original amplifiers there is Galil, DSPMC, CSMIO/IP-A (soon to be on sale) , Kflop with Kanalog. These will all control analogue amplifiers.
The pricesare in order listed, Galil being very expensive and Kflop/Kanalog probably the cheapest.
Your other option would be to replace the amplifiers with Step/Dir capable drives, probably the most suitable would be the bigger drives from cncdrives.com.
You will need encoders, your motors may have encoders already or it may have resolvers. There is a guy presently doing a mill with the Bandit Control and he will be using the original amps and a Kflop/Kanalog but his motors have resolvers and he is having to buy encoders that will fit on instead of the resolver.
You will find info here,
http://www.machsupport.com/forum/index.php/topic,21612.0.html Personally I think I would have taken another route rather than the Kflop/Kanalog but they do seem to work well for people that have them so maybe it would be a good choice, just not for me..
Hood