Every time I have to work around a deficiency in my setup I start reading the UCCNC manuals... I reckon that a UC300ETH/UB1 combination would be a drop-in replacement for my IP/M, which is a great piece of hardware let down by the software around it. I spotted that UCCNC does proper gantry squaring, although I haven't bothered to chase down exactly how. Would have to replace the MPG as well as I couldn't live without one of those.

Be interested to hear how you get on with UCCNC. At least it's a supported piece of software, unlike Mach3!