First, let me say many folks have the same problem you have. They can't get certain types of audio from certain sources.
A question which needs to be asked, what is playing your audio and it is the same for both Speakers and headphones, such as Bluetooth versions?
If you can click on and test all 6 speakers on your system, then that part is working.
Since I don't use most of the audio sources you reference, I will point you to Netflix and their explanation of how to get quality audio (link below). It shows to stream high quality audio you need a system that can deal with Dolby Atmos or a connection to an audio system supporting 5.1 surround sound.
What may be going on is, you believe 5.1 sound and 5.1 surround sound are the same thing. I believe, this is where the confusion starts.
YouTube stopped streaming 5.1 sound several years ago, so the testing videos may not work. Newer versions of sound are moving to what they call an Object in Space type version. The 5.1 sound, where each channel has its own stream, is no longer being done for these situations. But they stream info which provides the sound and along with that, the info as to where the object, and the sound it makes, is located.
Dolby Atmos has many requirements. One of those is a High Bandwidth during the sound reproduction. I have never been able to get the Dolby Atmos sound enhancement for speakers to work on my ASUS desktop, but it does work for headphones, if you have it available.
I am certainly not an audio expert, but I have been doing some research in preparation for a Home Theater upgrade.