Does HD sound better than the same track on regular services? When it plays properly, I mean.

I can definitely notice a difference. Everything sounds a little cleaner if that makes sense. 

Could it be sounding cleaner because it plays a little louder at the same Sonos volume setting?

There is a reason for asking this,  I will set that down in a longer post later.

HD Music has never established itself to be audibly better sounding in any volume level matched double blind listening test designed to eliminate bias or other variables from affecting the result. Not once. Anywhere in the world.

Why volume matched to within 0.1 dB? - because anything beyond that and the even barely perceptibly louder alternative sounds better to the human ear. This “louder sounds better” is a trick that every stereo salesman was taught in the times when there were HiFi brick and mortar shops.

Why the reference to the other variables needing to be ruled out? - because where the HD track has sounded better is where it has been remastered to a higher standard than the original; note here though that this treatment has till now been given to a very small fraction of the millions of recorded music performances out there. Most of HD music is just old wine in new bottles at higher prices. And where this improved mastering has been done, the same better sound is also available when the remastered track is downsampled to a less data dense stream that can be streamed wirelessly with far fewer problems. Proving thereby that the better sound is down to remastering/better mastering, and not due to the HD format.

So, with HD music what is really happening is customers are having to upgrade their kit, pay more for HD music, and then have their home wireless systems struggle to carry all that extra data around, especially in wireless grouped mode. And then, if they want stable grouped music play, to run ethernet wires between their wireless speakers to enable the denser stream to play properly. Ironic.

Note also that it isn't just Sonos that has a problem with this - the state of home wireless tech today is such that there isn't any make of wireless speakers that can today wirelessly do what you are seeing Sonos struggle with.

Further: none of this is news to Sonos. It is for these reasons that for years they resisted this HD red herring. But the marketing imperative of being able to tick the HD music box finally overcame their still valid technical beliefs, so now, voila - Sonos HD.

The ground reality remains unchanged.

That is all very interesting information and definitely deserves it’s on topic. As for my issues, I’m assuming “just wire them” is the best I can hope for. So Sonos released an HD streaming service knowing their speakers couldn’t handle it? That seems beyond idiotic even for the sake of keeping up with marketing.

Not everyone plays music on grouped speakers, so for such folk this isn't an issue where this service is concerned; and where you have this problem you may want to reconnect with Sonos and see if there is solution to at least getting the kitchen unit to play on a stand alone basis. And as I wrote, there isn't any other make that does not suffer the same problem that Sonos seems to do with HD music for grouped play. 

Also, not too many other makes even do grouped play of regular services as well as Sonos does.

More from @Corry P on this?

An issue may be your RF environment, not just WiFi but all radio energy impacting your selected channel. A simple WiFi checker won’t help here, you need one that looks at all RF energy in the target band, not just WiFi compatible signals. Not just average either, you could see a bursty signal that is causing issues at the peaks.

Taking steps to minimize your wireless data may help, search here for group coordinator for one method.

I found wiring all my easy to wire Sonos made a difference here, no HD music but the RF energy levels can get pretty bad.

Not really. Except that every customer is an isolated case, in some respect - the router used, settings, environment, etc. Sonos relies utterly on your network to operate properly, and in some cases something that works without issue on one system doesn’t on another.

Without knowing the details of the case and the troubleshooting steps taken, I can’t really comment further (I did look, but I see no recent cases).

@Corry P Granted the challenges in wireless grouped play of music using HD files, the OP issue with playing HD music on the single player should be easier to address? 

Indeed. I would think so. But if Tier 2 were unable to help in real-time with diagnostics, I’m not going to start all over again here - it wouldn’t amount to much, I’m afraid. 

I am not sure that OP has tried to work with Sonos to at least get the single speaker to play wirelessly. Over to OP.

I tried with the Tier 2 support to just focus on the kitchen issue. Again, no luck and again he said he could see no obvious reasons. It’s a mystery. 

I have opened a new thread linked below that might be of future interest to you:

https://en.community.sonos.com/advanced-setups-229000/stable-wireless-streaming-distribution-of-hd-music-6858832