Same problem with my Sony Blu-ray player as well. To play tru HD in usb the file has to be in m2ts format. Mkv won’t work. But this issue is solved using shield it plays every formats.
Congrats for your new shield. But I'm bound to continue use of my Sony X700.
I tried m2ts but again TrueHD not worked.
Have you tied it yourself? Which software did you use for conversion into m2ts?