Yeah it's not always as simple as plug-n-play (although sometimes it is) as there is sometimes device incompatibility, or settings need tweaking, or even wires needing to go into a different port.

FOR EXAMPLE
My Samsung TV just won't output surround to the Yamaha amp through the HDMI cables. I've tried all the ports and all the options and they just wouldn't play nicely. It'll happily route picture and stereo sound
HOWEVER
The TV does have an optical out, and will output proper 5.1 through there AS LONG AS we go into the TV menu and change the sound output from TV speaker to Optical. If I don't make this output change, the thing is working in stereo but not 5.1, so it can easily 'trick' the unwary listener. Luckily the amp display screen has little icons for each speaker, although they are small, so it's possible to see what it's doing.

It's a bit of a faff but it actually works, so this is how I do it.

Moral of the story - you gotta piss about a bit before you get the results.