So you have both Amps accessed as a single room in the Sonos app? Or two rooms, which you group? 

This doesn’t make a lot if sense. You can’t set up both Amps as surrounds, one of them has to be the ‘front’ Amp, which the TV would be connected to via HDMI-ARC. 

Most YouTube videos are down-rezzed to stereo. Often, even when they claim to be 5.1, they aren’t, even sometimes when you’re using YouTube’s paid tier. 

The 4 speakers are in the same room. 
 

i have 1 amp for front connecting e-arc hdmi, and setup the rear speaker amp as surround sound. I followed the Sonos instructions to setup  surround sound 

i have premium YouTube.

So, not ‘I set them up as surround sound’, just one Amp set up as surround sound, in support of the other Amp which is connected to the TV via ARC. 
 

Have you done any testing beyond this Youtube video? I’m somewhat suspect about that. Watching a movie would likely be a better test, my opinion is somewhat greater than 90 percent of what claims to be in 5.1 on YouTube is actually in stereo, due to the uploading process. You could look in the Sonos controller, and see what the system is receiving, it does get displayed. Do you have any other sources of  things to watch?

Do you have another streaming service you could try for test tones?

Try multiple tone sets even then, Amazon drove me to fits trying to get the top search for Atmos Test to play in Atmos... Yep, it was only Stereo despite the Amazon label.

Can someone recommend what I can use to test? Movie is hard because you don’t know when surround sound will happen. I have Spotify, Netflix, prime, YouTube premium.

also another question, when I listen to music is it possible to have all 4 speakers playing sound so  my open living space will have more music sound distribution ? Seems like it only play in the front

I’ve always ‘tested’ with the beginning of Saving Private Ryan. The bullets as they enter the water all around the viewer are striking. 

When streaming music, go in to the surround settings for the ‘room’, and change it from ‘Ambient’ to ‘Full’. 

Without knowing what services you have recommendations would be hard.

If you set your Surrounds to Full instead of Ambient [the default] they will play the full left and right channels, not just a filtered for ambiance version.

If the suggestions given still don’t produce music from the rear surrounds, then either the Amp driving them may be faulty, or you haven’t got them set up correctly as surrounds. If the former, you could try setting up again but with their roles reversed, or generate a diagnostics report and contact Sonos support. 
https://support.sonos.com/en-gb/article/submit-diagnostics

the suggestion doesn’t help. the diagnostic number is **************

Moderator edit: diagnostics recorded and removed

You should not post diagnostic numbers or case numbers to the forums. It will likely be removed by a moderator.

What you need to do once the diagnostic is submitted is to contact Sonos support, a call is far the best option.