Back when I did wedding videos I experimented with ac-3 5.1 surround on my DVDs. This was at a time, & maybe still is, where audio & video were separate files added to DVDA. It was an interesting experiment to say the least!
But now, 20 years later, I'm wondering if any of the rendering formats can render video & 5.1 audio for video streaming. I see where Vegas 19 Project settings can be set for 5.1 surround & the within the timeline, too, but not within the rendering templates I've see.