Having the problem with Itunes; My Itunes played all of my songs in just stero.
But all of other programs play in multi-channels.
You can fix this by yourself.
Open quicktime player;
Go to “Edit” > “Preferences” >> “Quicktime Preferences”
Go to “Audio” tab
at “sound out” choose the channels that suit your system.
click “ok” to close this windows
that’s all folks.