I've been watching this thread with great interest, hoping to find out that a drop in module is available for the M6. Would be a great way to get lots of light for a long(er) time, with some tradeoffs.
Seeing the Arc series (in the 2008 catalog downloadable from Surefire's website) and here in this thread, it is obvious that Surefire will not be making a conversion for the M6 host.
With the Arc series, I wonder what Surefire is trying to accomplish? In particular, what kind of magic are they using to get lots of light QUICKLY? Sure, HID's make huge amounts of light efficiently, but only after they've had a chance to get going. I don't see this technology being in step with thier mantra of using their lights as a defensive tool.
I also believe, based upon the design of the battery tubes, that Surefire has gotten wise to the modding (is it safe to call it an industry?) coming up with alternative power schemes. If this is indeed true, I give them a :thumbsdow.