I am using Magic Lantern on a Canon 550D. I have got a adapter to plug headphones into the AV cable. Problem is whenever I plug in the AV cable it thinks I am using an external monitor and the LCD panel on back goes blank;(.
This is more likely a question for the ML dev guys, but does it do that when you don't have ML booting from your SD card? Also, have you tried downloading one of the more recent builds besides the "official release?" the newer ones also give the T2i a full ISO range like the 7D.