To run your 2 x 123 lights on a 168S, you can buy a Pila 3.7 volt lamp assembly. It's interchangable with the Surefire P60 lamp assembly and works perfectly well with a 168S.
This won't work on the Executive series (different lamp assembly), but works on the 6P, G2, C2, etc.
I've read that the Pila 3.7 lamp assembly has more sidespill and less throw than the P60, but I can't confirm it.