I just unlocked my stock xt926 (Build 183.46.10 Kit Kat) using towelroot and motopocalypse. I then installed TWRP 22.214.171.124 (Kit Kat 4.4 build from Original development section) and did a backup of the stock ROM. I tried installing a couple builds of Cyanogenmod 11, but all of them get stuck on the red M. I got the latest snapshot from get.cm, as well as the one posted by epinter. I sent them over USB and used Ubuntu to validate MD5's using md5sum. I do a full wipe (of everything but internal storage) and install just the ROM, not Gapps, kernels or anything else. After a reboot, nothing but the red M. It will flash once every 5-10 minutes, but I let it sit for 45 minutes without anything else happening.
I also tried it in CWM6 (Kit Kat build from original development) and had the same results.
Right now I'm trying Gummy to see if it's just a CM thing, but has anyone else encountered this? If so, did you find a fix?