There are no pre-made triple MCPB for XM- series emitters. XP-L has a large die and a large dome, the dome does not fit under the 20mm optics properly. Trimming the optics results in less light out the front. Removing the dome results in less light out the front. Either way you still have a big die behind the optic - that results in lots of flood to go with all that heat. The dual triple XP-G2 offers a tighter beam and higher efficiency.
I doubt that the light as built is 6000 lumens. Maybe 4000 at startup in a best case scenario using that KK cell? See these posts:
djozz - Crash-testing a XM-L2 and a XP-G2 on copper Sinkpads (post #51)
HKJ - King Kong ICR26650 4200mAh (Gold)
Frankly now that you bring it up, this light seems like it would be extremely hard on a single KK cell, at least for the first minute or so. It might be best to use a high-drain Sony or Efest cell.