Upgrading to Sonos 5.0 setup for older Samsung TV - advice needed

Yes and no. In the Sonos app, you can go to more...-> About Sonos (or something like that) and then under the section for your playbase you'll see what audio format the playbase is receiving, However, you'll have to make sure whatever content your watching is actually in DD 5.1, as much content is PCM (stereo).

I'd recommend looking at the online manual for that TV to see if it does indeed pass Dolby Digital from the HDMI inputs to the optical out.

If it doesn't, then I'd take a look at the various HDMI/Optical switches that are discussed in this forum. I don't use one, so I can't recommend any one over the other, but there are tons of threads where they are discussed.

Thanks everyone for the replies. I've figured out a few things from looking in the about section of the Sonos app:

1. My Apple TV, which is connected to HDMI 1/DVI, appears to output 5.1 DD, but only if I manually set it to force 5.1 under Apple TV settings > Audio output > Change format on > DD 5.1. I'm not sure if I'm getting true DD 5.1 or transcoded stereo.
2. Mac Mini/Kodi media server, connected to ARC, will not output DD 5.1. I can't figure out if this is an issue with Kodi or macOS System Preferences.
3. DVD player on HDMI 3 outputs stereo, as expected.

At this point, I'm wondering what, if any, reasonable steps I can take to get proper DD 5.1 for all my devices. Would something like this switch work:

https://www.amazon.com/gp/product/B01GCGKLNQ/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

I'm not averse to spending an extra $60-$80 to get proper surround, a new TV is not really in the cards right now. I won't bother with the extra Sonos surrounds unless they're actually going to work as intended. Thoughts?

2. Mac Mini/Kodi media server, connected to ARC, will not output DD 5.1. I can't figure out if this is an issue with Kodi or macOS System Preferences.

MacMini unibody and newer (2010+) support HDMI multi channel out.

Kodi has some settings to control the output channels ,mixing vs pass-through, etc, but it's important you have the right media source. Apple has a built in utility called "Audio MIDI Setup". There, you can see the output devices (built-in speakers, HDMI, usb devices, airplay, bluetooth).

For HDMI, if nothing is actively playing, you should see toggle option for different 2ch outputs (which could be misinterpreted as the system only supporting stereo). However, if you have multichannel sound actively pumping out of the HDMI, it should show "HDMI Encoded" or something similar.

Keep in mind if you are outputting something not supported by the Samsung, such as DTS, the handshake will fail and revert to stereo. So assuming all the settings in Kodi is perfect, if Kodi is playing a DTS file, both the Apple interface and TV interface will only recognize stereo as the audio stream.

Use this to get an older Samsung TV to pass DD 5.1 from HDMI to optical: https://www.amazon.com/gp/product/B01M3SH3CL - you will need one per input that you wish to fixup - it connects from the HDMI source device to the HDMI input on the TV.