This answer gets way out of hand, but might have some useful tidbits for you.
You need a gcode generator that knows how to use a 4th axis - Carbide Create does not. You’ve solved this one.
You need a gcode sender that doesn’t mess this these gcode commands. I do not know if CM can do it. I know that UGS can.
On top of that, you need a grbl in between running on a board that knows what to do with it, and the steppers to do it. GRBL MEGA 5 is one, but at this point you’ve grown out of the stock control board. You can piece together a new board, etc, etc, etc an do so, but after 4 different boards, I settled on a more complete solution that included a board, and an well done ARM port of grbl. I’ve been using this one for well over a year: GRBL GRBL32 6-Axis CNC Controller F16 – 150KHz – Tom's Robotics
Here’s my first pass a an external drive setup with a keystudio board. Got everything in place, but shields failed all the time, and the documentation was terrible from keystudio. Steppers, Drives, Oh My! Adventures with replacement electronics and drives - #8 by stutaylo
The second try was a genuine protoneer board shield. That was ok, but kinda flaky too. Worked better than my first attempt at picking all the parts that seemed obvious, and seemed cheaper than more complex things like mach4.
Third try was an arm based board, from awesome.tech “superGRBL” - I liked the idea, but the CPU is soldered down, and managed to blow one up… The supergrbl code works, but it’s a mess to be honest. GitHub - paulusjacobus/SuperGerbil: STM32 driven ARM Grbl firmware. If I remember, this is based on yet another ARM port of grbl. Their dev was done an a 3D pro with a 4th axis ( ‘Maker’ Super Gerbil 4 Axis CNC controller – AwesomeTech) Seemed great at the time, but when I killed it, then repaired it, I realized how how unprotected the board was in some ways that I really didn’t like. With my tinker, can try #4. I think they have stopped selling this board, and were working on a replacement that fixed a number of my niggles about it - but that’s the last i heard about 18 months ago.
The fourth try was toms robotics, and I must say it was not the easiest to set up, but by far the most flexible. But having the code readily available with all the arduino board hacks out of it made it a lot cleaner, faster view into what was going on. The blue pill boards are cheap, they are pluggable, well supported, powerful, easy to swap out, I got it working well with a debugger quickly. It’s got scew terminals for everything, and clear labeling on the top and bottom of the board. I did run across a few bugs, but they were quick to resolve with Tom. ( GRBL GRBL32 6-Axis CNC Controller F16 – 150KHz – Tom's Robotics) I’m really happy with this board, the firmware, and it just works for the setup I have. I did have to do a few things to fix issues - my xl came with physical switches, and they were somewhat problematic. To use induction switches really requires ~7v. Anyone selling 5v inductive switches are selling “binned” parts (they test off the line as workng at 5v and go into a 5v bin) - the problem seems to be “works once” vs “keeps working” isn’t being well tested for, and I’ve had them work fine for a few months then suddenly stop working. So I wanted to run at 12v…but unlike the supergerbil board, high voltage isn’t supported directly, so needed to put together a tiny diode clipper (one diode, one resistor per switch pin - not hard, just a hassle that would be much easier done on the board. Read all about them here: Diode Clippers and Clampers | Circuit Types and Applications )