I have an install that was done in 2 1/2 months ago with a Sony XBR55X930E and a Sonos Playbar. It has an HDMI switcher (model unknown), a Spectrum Cable box, a DVD player, an Apple TV (model ?)
He started having the sound cutting out on the Sonos PB, he went into the Sony menu and turned on the TV speakers briefly then turned them off, the Sonos PB would work, for a while. Eventually the Sonos wouldn't work, he then turned on the TV speakers which are now starting to go out.
He told me he was watching Netflix when the TV speakers went out (after watching for an hour+). I need to confirm he was watching Netflix with the TV's App NOT Apple TV. If it was the the TV App then I'm thinking the TV may be the problem. IF it was Apple TV then I may need to look elsewhere.
He also told me he updated the firmware about two weeks ago.
I'm pretty damn sure the Sony has a hardwired internet connection.

I was setting up a x800e and shortly after the playbar started cutting out through the hdmi source, then at one point I had no sound. I made a switch to internal then external speakers on the Sony and the sound started up again. I believe it started cutting out later on, I then changed the output to pcm. The TV is on the latest firmware as of last Thursday. Sonos is also up to date.

There is a known defect with the optical output of Sony D and E series XBR's when output type is set to Auto and stream type is Dolby Digital. I've been hounding Sony about it for nearly a year. As of 4 weeks ago, their engineers had finally determined the cause and were finalizing a firmware update to fix it. "Soon" was the only release date I could glean.

In the meantime, the only fix is to set Digital audio output type to PCM only. Whether this is the same/related problem causing cutouts in the TV's internal speakers, I don't know. That could also be HDMI problems...

What mogul said

Thanks for the information. I was out at the site today. I couldn't get it to NOT work on auto in the audio settings so I just set it to PCM like you guys recommend. We'll see if that does it.
On a side note when testing the various sources I tried the Netflix button on the Sony remote and it said the TV wasn't connected to the internet. But when I went to the Netflix app icon it worked. I went back and tried the dedicated button on the Sony remote and same thing again. I did follow the set up button from the dedicated button and then it worked. Weird, I guess it is somewhat separate from the app icon. I also found the internet connection was on both WiFi and it was also hardwired. Not sure if this could cause weird things to happen but I turned off the the wifi connection.