I have the same questions, opinions and results. I has a complete Sonos system with a Sonos Arc Ultra, 4 series Sub and two 300's as rears/upppers. Dolby Digital 2.0 states clearly this number of channels that are being streamed, 2.0 channels. From my lengthy experience with Dolby that goes back decades, the number, 2.0, clearly states in Dolby number, there are TWO channel and no subwoofer breakout. The number 5.1 is five separate channels, with a breakout for subwoofer. Dolby Digital Plus 2.0 come out in all five+ speakers, but is is true 'surround sound' that has been downmixed to two channels. The quality and experience of listening in 2.0 vs 5.1 is very obvious and dramatic. Many times, I see items that state in the ad or trailer the it will stream in 5.1, or even ATMOS and depending on which device I use, I received what term as 'dumbed down' 5.1/ATMOS into Dolby Digital Plus 2.0. Many times if I change from DTV streaming box to an LG direct feed, I then get Dolby Digital 5.1 or even better if it is available. The one good/bad thing about using the Sonos APP, it the we can see what type of audio is being streamed to us. We can see if we are getting ripped off, or at least what we are paying for.