paulrbreers, I read his post very carefully and got it clearly. And it makes no sense to go from Surround -> TV. "Surround" has to be the last link in his chain unless he wants to bypass the TV. A surround speaker system- cheap or not- is no source of anything that could play on his TV if its "->". Yes, some come with pass through, but his does not. So it's obviously meant to be last link in the chain.
In his followup he confirms he's got other things playing from tv -> surround, so I interpret that as

TV->TV->Surround or
🙂apple:TV (hdmi out) to (hdmi in) TV (hdmi out) to Surround.
OP, since you appear to be confirming that other sources like cable/satt will play sound through your surround sound system, it appears the TV is passing sound through. Can you recall an audio setting when you first hooked up cable/satt that "enabled" pass through? If no, try temporarily switching the

TV HDMI cable from the HDMI in jack you are using now to the same HDMI jack to which your cable/satt is attached (just as a test to see if there might be a pass through TV setting associated with the HDMI ports). Then try playing things again through the TV (to the sound system). If that works, there's probably a TV menu audio setting tied to the other HDMI input (you're currently using for

TV) that would enable sound pass through. You'd need to look through the audio menu for something like that: "enable pass through" or similar.
If not, try 1+ experiments:
1. Go into the "apps" in

TV and open (movie) "trailers". Play them. Does sound come from the TV speakers or from the "surround" system? Try a few trailers, not just one. See if you can find at least ONE that will play through the surround system speakers.
2. Go into the youtube app and locate a music video. It's likely in stereo (for audio). Play it. Does sound come from the TV speakers or from the "surround" system?
3. Temporarily cut the TV out of the equation by going direct from

TV to the surround sound system. Does it play your music with a direct connection?
Such experiments can narrow the possibilities. For instance, by cutting the TV out of the chain in #3, you'll get a bigger sense that the problem is probably centered within the TV part of the chain.
Note also, that there is an explicit setting within

TV settings to use or not use Dolby Digital. If that's off, your TV is receiving only stereo and may only pass through to the surround system when it has a surround stream. Be sure to check that

TV setting too. It might be as simple as switching the option in that one menu.