You know, what you could do is get a AA2 light then just purchase the head separately.
Potential problems you will encounter:
1. protected 14500's will be a "tight fit" when using them in the AA2 tube with the high voltage head.
2. using unprotected 14500's will run the risk of killing the 14500 closest to the head. (Quarks will suck the juice out of that one)
Benefits:
1. Better runtime than using 2xCR123's.
2. Has the option of using two regular AA's but wont be a bright as the head is for high voltage.
Possible alternatives:
1. 2xCR123 body and use 17670 cells, excellent runtime, similar output with the high voltage head, plus smaller than the 2x14500 setup.
2. Low power head (4.2 volts) then AA body using 1x14500. (this is how i rock my Quark (and most people here i guess))
3. Turbo Head (high power) and AA2 body w 2x14500
4. Turbo head (low power) with AA body w 1x14500 cell
If you just take caution on the voltages of the cells you use, you can pretty much setup your quark any which way you want.