If I create an AAC file with 7.1 content, it will not play correctly in MPC-HC. (You can hear the sound, but it's distorted).
(I created the file using neroaacenc)
While playing the file, if I hover my mouse over the FFA icon I see this:
ffdshow audio decoder:
Input: AAC, 6.1, 48000 Hz, 39 kbps (libfaad2)
Output: PCM, 6.1, 48000 Hz, 16-bit integer
Change the ffdshow configuration to use libavcodec instead, and it works perfectly.
After MPC-HC investigations, it seems this is an ffdshow bug.
Find the MPC-HC bug report here: https://sourceforge.net/apps/trac/mpc-hc/ticket/1604