Only if the source you’re watching is encoded in Dolby Digital. Most TVs, and certainly the Sonos don’t do any changes to the source content. The Sonos plays what it is handed by the TV set. 
 

What are you watching? 

Gladiator on Netflix

If I try watching something on Vudu that is encoded with DD, will that that then be displayed as DD on the app?

Hmmm. And I’m assuming that shows as Dolby Digital in the description, so it should be coming across that way. What device are you using to grab that Netflix content? Are there audio settings for that device and/or app? I’m not familiar with a KURO plasma TV from Pioneer, but it’s conceivable that there are either. In fact, it may be helpful for you to post the audio settings for both the app you’re using to access Netflix, and the TVs audio settings. 

Frankly, I’m also somewhat worried about the age of a Plasma TV and the ability of it to pass Dolby Digital out to the Sonos.

It should, if the TV is sending DD out to the Sonos. Sonos will display what it is handed. 

All apps are from roku

Switched over to Vudu to watch Saving Private Ryan. Movie is in DD PLUS. Therefore, that should change the app to read DD no?

Are there settings in Roku that I should check/change?

Ok. Went into Roku and changed settings for audio to DD. Sonos app is still displaying Stereo PCM. 

Yes, it should change the format displayed to DD Plus. What you’re various tests are suggesting is that either the Roku device, or the TV itself is not passing all codecs through to the Sonos. 

Have you checked the TV’s manual? Can you post a link to an online version, so we can both read, and know which 60” version of a Pioneer TV set you have? 

Have you called Sonos Support directly to discuss it?

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

From memory the TV only supports 2ch PCM pass through, I swapped my Pioneer plasma for a Panasonic one because of audio issues to an AVR but this was a very long time ago now.

Edit…

The TV’s optical out may work for you using the hdmi / optical adapter.