I didn't know they were out of business. That's really too bad, but I guess there aren't many of the older machines around that use steppers anymore so their business probably went away for them. They saved my bacon years ago on my Bridgeport. And BOSS 6 is steppers, not servos.
Before I went to the AH-Ha design drive setup I used a card from Slow Motion Controls. It was an interface card and ran off a PC and used the Ah-Ha software. I'm not sure if they are in business now either, but if they are maybe there is another software that their card could interface with and run the machine off of.
Ocassionally I see the old BOSS machines for sale for very cheap............and I mean cheap. I was tempted to get one but now that I know Ah-Ha is out of business I'll think twice about that. I do have lots of Universal Quick Switch II tool holders for one. I'd sell them, but I got lucky and found an adapter for my R8 spindle and can use them in my manual.
I wish I could help more, I was in the same position years ago with my BOSS machine.