No. With explanation.

The analog inputs on the Port have, at the very least, a 75ms delay in order to buffer the input for playing in sync across any Sonos rooms. So if you were to use the Port to accept the output from your Marantz and then drive some Sonos speakers as surrounds, the surround information would be delayed from the sound coming from the TV.

Sonos does not make any equipment that allows you to take input from a non-Sonos 5.1 system, and use their stuff as “add ons”. They want you to use only Sonos equipment for the entire setup.

Thank you so much for your clear and concise answer! I kind of assumed there’d be a delay, but was told by a friend - and even Sonos tech support - that the Port solved that issue. I was skeptical, so I came here. 

Your answer is the best explanation I’ve ever read on the issue and it’s annoying Sonos does make that information more obvious/available. It’s all to get you in their ecosystem, like you said. 

Anyway, thanks again!

Heh. You’re welcome. I’ve got mixed feelings about that kind of “requirement” from Sonos, but honestly, many other companies do the same thing, and make it hard to put together a mish-mash of items to create a unified system. Often, due to the design choices made in the software. Sonos is no exception, they chose to make a whole home music system be where they hang their hat, long before the concept occurred to supply sound to a video source. Some of the choices made in the early days (which are inevitable, and actually are intelligent) block some other applications of their tech.

It would be nice if it were different, but here we are :)