Yes, to get a lower delay, you need to use the digital input, which applies only to the speakers in that Sonos ‘room’. All Sonos analog line ins have the 75 Ms delay as a minimum, it is the way that Sonos buffers the signal to play in sync across multiple Sonos ‘rooms’.

I don’t know about other soundbars that much, this is a Sonos forum, most of the users here would likely be bought in to the Sonos ecosystem. You may want to seek more information on a more generic, non-manufacturer sponsored forum. 

Great so the option is there to have the sound to play only in a local room with a lower delay of 30ms… now why would that only be digital and not on the additional line in input? 
I would like my stereo paired Play:5 set to play only in one room with the minimal delay. Thats all. 
They have the technology. Would be great to test this in a beta… 

Probably the cost of rewriting the entire suite of Sonos software for little benefit would be my guess. All of the Sonos ‘synchronized play in multiple rooms’, the basis of their entire existence as a product, is predicated on this function. 

There are lots of other options for speakers that aren’t designed for whole home music use that would likely be better choices. 

I suggest you read the eleventy five hundred other threads on this issue, it’s been explained very thoroughly many times before.