Since nobody else has responded...
Usually 1 battery lights that are CR123 only can use RCR123s. For example, my quark minix 123. It overdrives the light such that it is definitely brighter but gets hot quicker. But the drivers are good enough such that an extra 1.2 volts won't make that much of a difference.
However, with 2 lights in series, you are taking a light made for 4.3v up to 6.0 volts and feeding it 8.4 volts. That is significantly over the limit for a 6v driver and could cause problems.
I dont have that light nor experience so someone else can probably answer more precisely, but before you try it, I wanted to give you the heads up.
