How to play Dolby Atmos

Will the playbar play Dolby Atmos?
No way. PLAYBAR supports Dolby 5.1 (AC-3) or stereo PCM.

You'd need to downmix to something PLAYBAR can understand.

Welcome to the club. This is a huge glaring deficit with the Playbar. There's a thread here called 4K Blu-ray players and decoding from DTS to Dolby Digital. That's the only way you're going to get any kind of surround sound out of this expensive soundbar. So far the only 4K player that does this is the Samsung K8500.

Many of us are hoping for a software change when they release the new so-called Playbase, which has had pictures and a purported price leaked, but not officially announced, and no significant information on features. The question in my mind is, if there is a new software release at that point, will it do Atmos or DTS or whatever only on the new device, and not the old Playbar, because there's not enough processing power on the old device?

Sonos has done an outstanding job in the past keeping everything backwards compatible, but this may not be possible if there is a requirement for additional horsepower to do something more than Dolby Digital.

I'd be happy to be a beta tester for this upcoming device, if that's a possibility 🙂

Unfortunately, that's not possible. The optical port doesn't have the bandwidth needed for DTS or Atmos. It requires an HDMI port.
So, it looks like we're left out in the cold with out of date standards.

I've seen other posters who indicate that the optical port can indeed carry DTS at least. I'm not an expert.

Here's the quote from Wikipedia, that bastion of truth:

S/PDIF is based on the AES3 interconnect standard.[1] S/PDIF can carry two channels of uncompressed PCM audio or compressed 5.1/7.1 surround sound (such as DTS audio codec); it cannot support lossless formats (other than 2ch LPCM) such as Dolby TrueHD and DTS-HD Master Audio, that require greater bandwidth[2] like that available with HDMI or DisplayPort.