The dk45se had backhoe overheating issues in some heavy use instances, Kioti issued a fix for this, which involved repurposing the transmission case fill/vent, as the new remote circuit fluid return port, which allowed for less restriction in fluid return than the built in remote return. It worked well, and reduced fluid temperatures quite a bit during heavy operation.
Below is a screen shot of the kit and part numbers. Important note is the new breather vent location, as the old fill/vent is now in service as a quick connect return port. Perhaps some of the methods or parts may be useful for your NX.