blademan,
Have you considered just using one cell and dummy battery in the LX? The reason I suggest this, is to drop 6V down to 3V for the adapter means the resistor will be consuming as much energy as the Luxeon. I don't think the Inretech is heatsinked well enough to overdrive it much, so you'd want to stay pretty close to the original current on 2AA cells.
A ball park figure would be ~7 ohms, but even at 300ma (0.3 amp) the ristor will be eating ~ 2.1 watts. You'd really need to test the resistor value for your particular Luxeon's vfd (forward voltage drop), as every 0.1V above it translates in to about 100ma more current.
Safest way is just use one CR123 Lithium cell and a dummy.
