seems like a lot of routers out of China come with NC-studio which uses a PCI card to control the machines via a 15 pin cable.
I just picked up a used 1200x1200 machine with the aforementioned NC-studio and got it running and did a test cut with the last tool path I ran on a smaller mach3 controlled 500x300 machine and it was quite disappointing - lots of dwell marks and odd lines in the surface - admittedly this was a 1/72 scale model plane part which isn't what the machine was designed for but I figured it should be able to do a bit better.
So I wired a Mach compatible breakout board to some ribbon cable hooked up to a 15 pin D connector (so I didn't need to modify anything in the machine), set up and tuned the motors (7000mm/min rapids which is pretty good and maybe a bit fast) and re-ran the part. It's basically identical to the part made on my smaller machine.
Here's a comparison pic -
Mach/smoothstepper 500x300 machine on the left, Mach on the 1200x1200 machine in the middle, NC-studio on the 1200x1200 machine on the right.
The results speak for themselves and I'll be permanently wiring in the mach breakout board...