USB doesn’t suck - I guess you’re using a PC (running Linux as your host? You haven’t provided sufficient information to know or what flavour of Linux) which is challenging to get working reliably with USB.
I haven’t heard of anybody successfully using an Ethernet connection between the host (your PC) and a main controller board although a few have tried but I can’t find any indication of success:
Regardless, I just spent the better part of an hour trying to find the schematics and pinout diagram for the the board you’ve illustrated above (your marked up image seems to come from a Reddit post). With no luck.
I was also searching for a serial wiring diagram between the main controller board and something like a Raspberry Pi. Again, with no luck.
There seems to be some confusion as to whether or not Kingroon uses the board in the image or an MKS Robin Nano (or “Mini”) or if the schematics used for the Kingroon board are the same as one of the Robin variants.
Going back to the question at hand regarding getting Klipper running on your printer without problems, here are your options:
- Use a Raspberry Pi or some other Single Board Computer (like from BTT or Orange Pi) and using that as your host. I can guarantee you that the USB interface will be fast and easy to set up as well as being reliable (regardless of the host board or the main controller board used).
- Rather than Ethernet, try to connect your main controller board to your PC using a serial line. Again, I don’t know what your PC is so I can’t comment on options. You will need to find schematics and a pinout diagram. This will take some time to get working and my not never work completely satisfactorly.
- Continue with the Ethernet connection. You will need to find schematics and a pinout diagram. I would say that this has the lowest probability of getting Klipper running without problems.
So, it comes down to whether you want a working printer or you want to do a science project with a poor chance of success.