Hi @Dieguito
Welcome to the Community!
We do, in fact, already “up-mix” all TV stereo sources to surround sound. This does not mean that you will hear all the audio that comes from the front out of the rear speakers too - some sounds will come from the rear while the majority of the sound will come from the front.
It is possible that you won’t even notice the effect depending on what is playing and the quality of what is playing, and the level will be low - it’s more to bring the soundstage forward a bit rather than to emulate true surround sound. If you place an ear close to one of the rear speakers you will hear some audio.
There is no way to adjust the effect short of adjusting the surrounds level for TV audio (Settings icon » [room] » Surround Audio » TV Level), and there is no way to have the same audio play from the rears as from the front - the only way to do that would be to have them in a separate “room” in the app and grouped with the Arc Ultra.
I hope this helps.