To use the existing interface and control box requires the propriatary interface card. chances are it requires one of the older isa cards. So, unless you're lucky enough to find one cheap(btw when looking for one, it doesn't matter if the card is described as for a mill or lathe, they're the same exact card.) However this is a longshot.
given that these steppers are deceptivley underpowered (barely 100oz/in), inefficient, not to mention the fact that your processing power is going to be limited by the requirement of having a "legacy" isa port, i can see only one reason for holding onto the setup as is, and that's if you have a lathe and still want to single point threads. that's the only reason i still hold onto 1 card.
save the headache and get a 3axis controller and stepper kit from any of the many vendors. you'll spend much less than $600.00 and have a much better machine.
Forget the Spectralight cards etc and just get a Xylotex board and power supply. Also upgrade the steppers to bi-polar if you can swing it. I updated my Spectralight mill with the above and it works well. Been using TCNC in DOS for now but am about to make the jump to MACH.
I got the mill of ebay hardly used almost like new for less than $300 delivered without any black control box or cards, software etc. It did have the vice and one 1/8" collet included lol.
When all was said and done I think the whole package cost me $580.00 to be up and running. So for a few hundred $$ you can get a xylotex board, I got my PS from MPJA but xylotex has them now also I believe and I got some surplus motors from xylotex with my order as well ( these are not the strongest steppers 120 oz. I think but they are ok for the sherline, I may be looking to go with 260+ oz. motors in the future or at least one for the Z axis to try).
By the time you buy all the updates the spectralight people will sell you you could probably have just gotten a brand new cnc ready mill direct from Sherline with the PC heh.. Yes they are that over priced!!
Good luck with it all. Retro fitting the existing setup as easy as pie btw. But have to figure out how to run the speed control I still use within the case via software.
if you figure out that speed control, let me know. the only thought i had was run the spindle as the 4th axis with a stepper.
but about the spectralight, xylotex is a great choice. however, just about anything is better than what you got. check out probotix, amongst others. if you don't mind a little soldering you can do it for under 200.00 (plus p.s.) from hobbycnc.
for power supplies just look for a linear 24vdc supply that puts out 5+ amps. i'm running a 3.8 amp supply and haven't had any problems.
Something is always better than what I have lol.. It works ok thus far and yeah there are lots of options out there to choose. But I got up and running for five bills and some change for everything, how many lurkers and newbies wish they could pull off the same
that's cuz you got a screamin deal on the base machine, hopefully billy b did the same. he might be feeling ripped off right about now and needs to realise that chances are he bought a fairly decent sherline mill with it's own enclosure and with mounts making it cnc ready, so unless he paid a bunch of cash for it, he did allright. myself, i paid 650.00 for my spectralight0200, and fairly used at that. then again mine came with the card and control box which i subsequently sold at auction for 180.00, so not too bad.
btw billy b, that power supply you have might even be useable for whatever board you get. it's output is 48vdc, not sure of the amps, but i'm sure it's got em to spare.