HELP NEEDED - Bigtreetech BTT EXP-MOT + SKR V1.3 Firmware setup with Marlin

[Phinieo]

Hi 3D printing community,My project for the last few months has been 1.0M x 1.2M x 0.4M huge 3d printer. I've been having trouble lifting the massive printbed which I've attributed to issues with stepperdrivers which until now has consisted of a single TMC5160 driving 4 steppers in series.I came across the Bigtreetech BTT EXP-MOT a few weeks ago which would evidently solve my problem of not having enough stepper driver slots on my printer board which is the SKR V1.3. Unfortunately I cant for the life of me figure out how to set up the expansion module in the Marlin firmware and support online is pretty limited. I contacted their support and they said"You need to define the pins according to the pin diagram of the module and the EXP port of the motherboard. Then add the definition in the pins file of the motherboard firmware."Unfortunately all my attempts to do this have apparently been wrong. I came across a forum which said there was a single header definition line in my Marlin code that would make them functional but this didn't work either.Has anyone used this and had any success? Any help or guidance to give?I've attached an image of my printer cause I think it looks pretty cool