I will assume that the drives/amps need a +/- 10v analogue signal, so your options are reduced to a few different controllers if you wish to keep them (I would recommend you do)
The options are
CSMIO/IP-A
DSPMC
Kflop with Kanalog
Galil
I only have experience with one of the above controllers, the CSMIO/IP-A but I love it. For a lathe however there is a drawback, there is a delay in the pullout at the end of threading which cuts an annular groove. If that is not a problem to any parts you will thread then I would say it would be a good choice.
I know the guy that did the Galil plugin for Mach eventually found a way round this issue but how I have no idea.
Not sure if the DSPMC and Kflop also suffer with the problem or not but it is only present when using full encoder for threading rather than the more common single pulse per rev.
Here is a vid showing the small lathe I had which was fitted with the CSMIO/IP-S (Step/Dir rather than analogue) I am just demonstarting the threading by rotaing the chuck by hand to show how it follows extremely well.
https://www.youtube.com/watch?v=0-KlHFYxzkMRigid tapping is also possible with the CSMIO/IP-A and S controllers, never did it on the lathe but here is a vid of the Chiron I have which uses the CSMIO/IP-A
https://www.youtube.com/watch?v=GNL2XdsJz2ETo do rigid tapping and lathe threading with the CSMIO you also require the Enc Module and if using a handwheel you need the MPG module. With the MPG module and the CSMIO the handwheel will be like you have on machines like Fanuc, with Mach and most other controllers the handwheel is quite a bit different and not as nice in my opinion.
Now your encoders may or may not be an issue, it depends on their output, if the are the uAmp or 1vpp type then they will be no use with the CSMIO and would need replaced, likewise your handwheel. If they are 5v square wave then they will be fine.
Hood