In fact I do not have a Shapeoko3, but instead an X-Carve, which I bought back at the end of 2016, before they changed it to have a single square gantry rail and I kick myself constantly because the flex is way out of control! It does however run using the same sort of Arduino+GRBL setup and so naturally PixelCNC has a GRBL/Mach3 post. There is a post-processor system and a few other posts that I haven’t personally tested but I tailored them specifically to the specs for the controllers that users reported needing support for.
The current free trial limits input image size to a total area of ~65k pixels but I will be releasing v1.30a today which removes that restriction and instead imposes a 10 minute session time and a limit on the number of tool motions per operation in exported G-code. This lets users test out PixelCNC’s ability to handle higher resolution images properly.