For a 90 min movie, a DTS 5.1 core (1.5 Mbps or 1509 Kbps) would have 1 GB for audio within the file size.. For the same movie, DTS-HDMA 7.1 (4.5 Mbps or would roughly take 3 times more file size (3Gfor audio..
I have watched the same movie with DTS & DTS-HDMA and HD audio is defnetly better.. A recent movie which i saw was "Adrift"..
If you want to check the difference, try the same movie in different audio streams..
I think even though your MPC audio settings would be right, windows might be doing something there..
Try Kodi too, under audio settings, you need to choose "WASAPI" and play both files back to back and check the difference..
BTW, which AVR do you have & what is your connectivity between AVR & source?..