I don’t have the 6600 drivers but I run TB6560 at full power (3 amps) for the X and Y axis. Only the Z is set lower. I’ve run these drivers with both Marlin/Ramps and Mach3 motion controller boards. You said that you’ve used the same electronics before without issues but were you running 2 motors off each driver then too? If not then you definitely need to take that into consideration. I can run my X and Y axis for hours at a time and motors barely get warm with TB6560 drivers set at 3amps.
Like Vicious said, this probably isn’t then best place to ask for help with non-standard drivers, firmware, and board too. I agree that the heavy router, huge build area, and elevated platform is a worst-case scenario. Hope you figure it out.