so yeah, i downloaded a 720p mp4 file that plays great on my appleTV (2010), except that surround doesn't work. i understand that this is probably to do with its audio track being a 6ch AAC, which my awful old receiver probably can't handle (it's connected via optical). how do i get it to output in 5.1? (also, VLC seems to think the file is stereo, which is weird). thanks in advance!