6A is doable with a single cell and XM-L2. I have a C8 at about 6A and an Ultrafire F13@ 5,9A and some other lights running similar emitter currents but with more emitters and cells (same principle though). Ill show this thread again showing HD2010@ 5,9A.
When that is said, it requires a freshly charged cell@ 4,2V like Samsung 20R, green sony and such and all resistanse mods in the book in order to see 6A. Having proper DMM wires is crucial..
You could verify your DMM/DMM wires combo with a bench setup without a driver circuit. Just wires from the battery to an XM-L2 on copper (attached to some heatsinking). You should be able to see 6A if you have something like a Samsung 20R or Green sony 26650 freshly charged to 4,2V...