Have you checked that all your speakers are in phase? Specifically that the positive on amp cable goes to the positive connect on on the back of the speaker?

If your system is otherwise matched especially the left/centre/right then it should function.

Depending on your surround sound amp/processor some of them can get stuck in stereo vs surround.

A quick test is here.

Verify the dialog with a well mixed movie or dvd though that adds another level of possible issues. (most appletv stuff works as expected)

Good luck with it.