Brand new to the site.

I inherited a Sieg X3 CNC mill with X, Y, Z, lathe, and rotational stage stepper motors and a spindle being driven by a KBMM-125 controller.

It is currently running on an old Windows 7 machine through a parallel port BOB.
Spindle speed control is only via a pot on the front of the machine.

I am looking to upgrade the BOB to a USB connection so I can use a new laptop to run it.

Control software is Mach3 on the old machine and I've downloaded Mach3 on the new machine and have the license file moved over.

I am having trouble finding a USB BOB that has 5 (or 6) stepper axis, runs through USB and has an analog output to drive the spindle through the KBMM-125.

What I think I need to do it get such a board and wire the 0-10v analog output into where the speed control pot is on the KBMM-125.

First, am I approaching this correctly?
If so, any recommendations on a BOB?
Ideally, I'd love some help with a wiring diagram for the spindle control, but if I have the right card with the analog output, I think I can figure that out.

I've seen the C6 board that uses a stepper channel to make an analog signal, but I have 5 channels already and figure it's easier to just get a board with the analog output native to the board.

Thanks for any help!
Cheers,
Mark