I think that board has transistors for outputs. You need 2.55 ohm resistors, at least 10 watts. Probably you can find some 10 watt power resistors at
www.mouser.com
Don't use the 1 ohm resistors unless you are using 1 per motor, in which case it needs to be 20 watts. If you are using one per motor, then it's probably ok.
If you are using Turbocnc you need to run it in DOS mode, not a dos box. Click shutdown and "restart in dos mode". If you are running it in windows it will be just as rough as Kcam.
Slow the cut speed down a bunch and see if you are making better circles. It sounds like you are loosing steps.
Eric