CNC upgrade

Hello to all you professionals

I have been following all subjects for about four weeks now, I find it very interesting but I must admit a lot of the electronic & technical stuff goes over my head.
I am running a far eastern mill 13" X 5" travel with 3 type 34 steppers 2 1/2 volts, 4 1/2 amps (27 amps total running) with 2R0 50 watt resistors, 10tpi leadscrews direct drive, unchecked ( no encoders) max speed 7"p/min and using a compucut program (HPGL) and interface in unipolar mode, I had loads of problems with missing steps and interference between axis when I first set it up, until everything was screened and a good interface cable was used. It has been very stable, and has ran successfully for about 2 years, At 10 volts I can run all day and the motors just get warm, but I can push it up to 12 volts for a couple of hours or so if I need the extra power. It has served very well for the type of work I have been doing.
I would like to upgrade the programming department ( at present running on an old 386 SX 33 with DOS 6.22 ) , are there any packages that would run with this interface, or would I have to upgrade to a bi-polar device, I would prefer 4 axis if I had to change the interface, to include the dividing head (any idea of costs).
If I had to change the interface, I would use the old one on a Sherline Mill which I have standing idle at the moment, so it would not be wasted.
I like the sound of linux and emc for the future, but it does seem a bit complicated to set up, I priced linux 5.2 locally here in the UK, it came out at �39.50, but I think I can Get it cheaper as a friend got version 6 for �25.00
I have no other experience in electronics, computing, or programming, other than creating the above conversion, but learnt a little in the process.

Yours Faithfully
Peter Smith