It has been I while since I have done both fire/smoke, didn’t PRT Fume used to report Fuel/Fire values? I can’t remember, trying to do some kcm coloring seemed easiest to through a switch in there control via fire.
Magma should be able to read the Fire or Fuel channels. You should just make an InputChannel node and set the name to Fire or Fuel depending on what you want. Of course it will only work if you actually saved those channels into the FumeFX simulation file.