No. The A/V outputs on a Port are standard line level outputs designed to connect to an amplifier. They would not ‘recognize’ and change to a subwoofer output. It would be the same as connecting your subwoofer to the back of a tape deck. 

If you have your Port connected to a standard receiver, you could connect your subwoofer to that receiver, assuming it has a subwoofer output. 

Hmmm.

But what about a subwoofer with a built in amp?

I have no use for a full amplifier as Sonos app does the job for me. 

Return the Port and get a Bluesound Node 2i as offers sub-woofer connection

If your subwoofer has RCA inputs, they it would produce sound, assuming it’s got it’s own amp, play the right frequencies etc.  I have never set up a sub that way, but believe it should work.

However, I don’t really think that’s the main issue.  Your port is not part of your Sonos home theatre (HT) room, it is it’s own room.  You group  the Port with your HT to play audio, rather than bond, like you did with the Arc and ikea speakers.  When rooms are group, music sources are delayed so that all audio is in sync.  When playing TV audio, the HT room plays the audio immediately to be sync with video, but other rooms are delayed to accommodate multiroom audio.   In short, using the Port +sub with your HT is going to result in an a bass line that delayed behind your other audio, creating a weird echo.

Also, your Arc will not adjust the frequencies it plays, leave bass notes to a sub, because it will not know a sub is there.

Whilst that certainly does look impressive, afraid I am fully invested and committed to Sonos for the next 5-10 years. 

This is more or less what I thought might happen. Thanks. 

So- the Port output- what's it for? What purpose does it serve?

Right now the Port is just a very expensive receiver for my turntable (which was also expensive, because I needed one with a preamp!). I have also used it to bring my Projector into Sonos, although I only get stereo sound.

The purpose of a Port is to turn a conventional HiFi set up (amplifier and speakers) into a Sonos streamer.  The line-in is a subsidiary feature, and not the primary purpose of a Port at all.  You are right - it is a heck of a lot of money just to attach a turntable, but that isn’t really what a Port is for.

The fact that is designed to work with a HiFi also explains why you get only stereo sound - it is not designed for AV applications at all.

It's an awkward little device, isn't it? Why would somebody want to use the Sonos ecosystem if they don't have Sonos hardware. And all the Sonos speakers already talk to Sonos app.

I suppose it services people who have Sonos in some rooms and a Hi-Fi system in another. 

I think it would have been better value had they tossed in a Bluetooth receiver (even though that's not Sonos' brand). Then at least people like me would have another use for it.

(It actually does have a Bluetooth receiver in it, because you have to use Bluetooth for the initial set up. Maybe I should demand a firmware update to utilise the embedded technology)

Make a Sonos version of the Bluesound node 2i    with no distortion of the digital variable output and I can guarantee them at least one sale. . It’s like they just completely ignored all the competition when they built the port. They will get sales from people in the Sonos system but if you are just starting by looking for a streamer for Hi-Fi it is not competitive on price sound connectivity or formats. 

I must admit- I have no complaints about the sound quality I get from my turntable via Port.

I do use the high bandwidth 2000ms delay though, to ensure quality. Which can be a bit disorientating when you lift the needle and the sound carries on for 2 seconds.

Using the fixed volume line out gets rid of the distortion I was getting from variable output but means I’m for ever switching between fixed and variable depending on how I’m using it Quite why they want to distort the sound to a Hi-Fi I don’t know. The spec is poor value compared to the market. 

Yep.  Like me, and lots of others (although I in fact have the Port’s predecessor, the Connect).

Sonos’ first products were earlier versions of the Port and Amp.  Sonos’ first all-in-one speaker came 4 or 5 years later.

Strange given their roots that Sonos didn’t produce a product competitive with other Hi-Fi streamers. 

I think you are missing the point. Sonos aren't trying to compete in the HiFi streamer market. They are providing a means to incorporate a Hifi in the Sonos ecosystem  I can't imagine too many people would choose it standalone.

And it's terrible value just for a line-in,  but it isn't marketed for that.  I always suggest people consider getting a Sonos Five instead 

I fully agree they aren’t trying to compete in the Hi-Fi streamer market. They are failing. But they are trying to sell a streamer that connects to a Hi-Fi so strangely enough I’m comparing it with Steamers that connect to a Hi-Fi. I do get your point though. It is aimed at Sonos customers not at Hi-Fi customers    In offering the Arc they have offered an upgrade to compete with the market so it shows that Sonos are more than capable and the Arc has been well received.   In the Port it is actually offering less rather than more. Hardly compelling or competitor and not surprisingly it hasn’t been well reviewed because it offers less than the competition.  Rather just a neat looking black box where it seems focus has been on the market appearance rather than the substance. Disappointing.