Besides all of the excellent suggestions above, there are at least two more options: 1) the goinggear.com MC-E Head for the SureFire M Series, and 2) the OpticsHQ TLS TX3 Conversion Head.
Choice depends on how much money you want to spend and the style of LED option you seek (and in the case of the OpticsHQ head, whether or not you like the two-mode UI). The LF and goinggear products are complete THs. Just remove the KT4 and replace it with the LF or GG TH. An LED turbo tower is basically an LED version of the incandescent lamp that comes with your M6. Essentially, any LED that can fit through the reflector opening can be used (I've built Seoul P4, Cree XP-G, and Cree MC-E towers driven by boost, buck, and linear regulator drivers). Led Zeppelin's stuff is in a league of its own.
If you are reasonably adept at soldering, you might consider buying a Netkidz tower kit, a 17mm buck driver from DX or KD, and an XP-G R4 on a 10mm MCPCB from nailbender and build your own. Total parts cost is probably less than $40.