The connection is usually like this.
cable box -> receiver -> HDTV
So that works great until you need audio from HDTV -> receiver.
For that you need an audio path from HDTV to receiver. The usual connection is from the optical out from the HDTV to the receiver then configuring the menus on the receiver and HDTV.
For APPS it can get tricky as on the Samsungs I ran into, the APPS would not honor the setup of the HDTV and in the app you would have to find it's sound options to change it there as well.
have oledb6 with xfinity cable box, denon air-x2200w receiver. all works fine running xfinity through denon, but when i switch to tv apps will only pull sound from tv. please help.