Firstly, a Sonos 5.1 setup is crazy expensive. Just looking at the online shop, a Playbar/Playbase, Sub and 2 surrounds (Play 1s) costs £1,736. You could easily spend that money on a wired setup, as well as an AV Pro to come round, trunk the speaker cabling, set everything up and then have at least £200-300 left to spare. It would support all sound formats, and I would say arguably give you slightly better sound (but it's negligible).
But set a Sonos surround system up, feed it a Dolby Digital 5.1 signal and it does a great job (as it should do, because it's crazy expensive). You can get a decent amount of bass without the Sub too (quite why it needs to cost £600 is really beyond me). So the "low quality Dolby Digital" comment is just pointless and incorrect. Sonos has superb software and the technology of SonosNet is fantastic, but comes at a hefty cost.
Saying "I actually use fewer wires" for a Denos/Q Acoustics setup just means you didn't do your research properly. Any LG TV will pass on a 5.1 signal either from an internal or external source (and most Samsung or Sony ones do too), and differentiating between "thick" and "thin" cabling is seriously clutching.
I fully agree that you can have issues if you're a serial DVD/Blu-Ray watcher, and I agree you can get pesky lip-sync issues. I'm wondering how many folk bought the last Star Wars films (DTS only for the main soundtrack, DD for description only!), plugged it in and realised they couldn't hear anything (although out the box, most TV/Sonos setups seem to default to 2.0 anyway). Lipsync issues though, in my experience, are more down to the TV manufacturer than Sonos (but it absolutely is a pain).
It is patently obvious that home theatre was an afterthought for Sonos, else there is no other reason to begin with a purely optical soundbar and charge £650. If I was a betting man, I'd give it a 90-95% chance that Sonos is R&D'ing a HDMI Soundbar. There is just no other way to take that product line forwards, but how they would make it work for surround sound is another thing. I'm guessing there would be serious bandwidth issues for anything beyond DD5.1 with non-wired surrounds.
And just 2 points to make to the OP - if we want to start talking about so-called "true" AV setups, then things such as clear speech shouldn't even be an issue and you should be watching everything in Pure Direct mode. If you're having to make adjustments for this, it's not setup properly in the first place (save for the odd show/film with really bad mixing).
Also, Sonos quite literally has a Speech Enhancement function!
And buying speakers such as the (excellent) Q Acoustics ones and then quite literally dumping them all next to each other on your TV stand with little space between them (thus, little audio separation) and at a low level which must be way below your ear level, is just wrong - you might as well have just got a Playbar.
I also must say the people who seem to be worried about sound formats, etc IMO is a vast minority of overall Sonos users. Every single other person I know who has it simply connects to their WiFi and is done with it. Most don't even know about DTS, DD+, Atmos, etc. And if you care that much about it, I find it odd you'd run through all these hoops to get surround sound and not want a "proper" wired setup in the first place.
Sonos is a music streamer and simple soundbar first, and an extension into Home Theatre second. It's the best in the market at the first, and does an admirable (if very very costly) job at the second.
Aside from having 2 surround speakers that will give you low quality Dolby Digital?