If you don't know how to override EDID, I'm pretty sure you're not doing it
I have the same issue as you, with Yamaha rx-v765 and LG PK760 TV. HDMI out from an i7 3770k PC.I fixed it - just so no ones trying to figure out what could be wrong.
I was fiddling with the settings on the AVR.
I do not know why, but I set the followin
HDMI control = ON
enabled sync in the Audio output settings
and woilla! I have DTS-HD and Dolby TrueHD - Now I just have to get a real movie or something to test with.
Thanks for the help