After starting down about elebenty-nine different paths with the, um, 'driver', then turning around and going back to the start, I finally settled on this:
Since they're all going to be in parallel, no need for the 3-section layout of the original, right? And the AO D436 has plenty of overhead for everything four cells can put out, I think...
(<--LOL)
So I double-stacked them anyway because hey, why not?
I've bench tested it and got 3.40 amps.
Here's what the driver does, as best I understand it (i.e., not at all). The MCU-like thing controls the single 7136, which doesn't see any of the output load at all, it's just used as a sort of relay to control the gate on the D436, as that FET needs more current to switch than the MCU-thing can provide (if this is not how it works, then I am completely lost and can't see why they didn't just delete the 7136s altogether and save a few pennies). The set of three sense resistors (original setup was 3 resistors and one '000' zero-ohm thing per D436, new setup is 3 '000's and no resistors) limit the current the D436 passes. Shorting across the zero ohm resistor pack does not increase the current, but connecting LED- direct to BAT- does, so I have no clue what part of the circuit is doing the regulatin' here. Who cares. If it does better than 3 amps to each of the 5 XMLs, that'll be... yeah. A lot.
The solid copper wire I added is for heat transfer, and also to tie together some of the unused pads to give more space to attach the LED wires so I don't end up trying to solder five wires onto one little pad. For the positive side I will probably drill thru the board at the 3 original pads and solder wires from the battery side of the board rather than rely on the almost certainly undersized vias in the PCB.
What's still left to do is: weld the threaded ring onto the heatsink base (I hope I'm not out of argon, it's been months since I touched the thing), drill wire passthroughs in the heatsink, and polish the damn reflector.
(I found this same 5x reflector at DX for I think 9 bucks, if anybody's curious- don't have the link but it's easy to find, in their reflector category)