Sounds the same to my ears. I no longer own a connect to compare however. 
 

Are you using the digital out?

I using the RCA outs (the same as I did with the Connect).  

I can’t imagine that Sonos would replace a product with lesser components. Just doesn’t make good marketing sense. I replaced a Connect with a Port and while I can’t say that there was a significant increase in clarity I didn’t notice a reduction.

As a note… RCA is an analogy technology that components used can themselves degrade over time. I would suggest upgrading the RCA cables to new. Also, unlike digital cables there is a difference in analog cable quality. 

With digital cables such as HDMI for example either the signal is transmitted correctly or it isn’t. Spending more than $50 on a 18GB HDMI cable IMO is money not well spent. In truth $50 is probably an unnecessary upper limit expense. The major priority is a tight connection. 

The best RCA cables are Solid Core_Oxygen Free Copper (OFC) non-twist. Each strand is individually insulated up to the connection point. These cables are generally priced around around $40 each on the low-end.

If you are using the same cable as before with the RCA out, and the connection is not loose the only way to get different sound is a defective Port.

Burn in periods are pyschological effects but they do not apply here in any case.

Are you sure you are not just getting influenced by what you read? Where does it say that there is a different sound when analog outputs are used, on variable setting?

Nobody said that about the RCA outputs. In fact this review suggested they were fine. 

The AK4490 DAC is well regarded, and I would say that the analog out quality is better than the old ZPx0/Connect.

I’ve seen a number of posts about the poor sound overall without regard to output.  

What Hi-Fi? said this:  

Unfortunately, however, the Port’s presentation is about as disorganised as a teenager’s bedroom. Nobody seems to know where their part comes in and how loud it should be, a combination of missed steps conspiring to confuse even the most seemingly straightforward arrangements. If your streamer cannot keep in time a constant 4/4 kick, control will rapidly slip from its grasp the more parts get planted on top.

That would be enough on its own, but perhaps worse is how uninterested the Port appears to be in whether you enjoy your music or not. Dynamic expression is poor and punch is so lacking you almost expect its corner to throw in the towel.

This is all the more frustrating because it represents a step back. The Port is cleaner and more detailed than its predecessor, but the Connect manages to tie music together and deliver it in a much more cohesive and engaging fashion.

It’s those latter talents that are most important, and the fact Sonos is asking its customers to spend more on a worse performing product is a real disappointment.

Using an external DAC is helpful, so if you have a decent one built into your amplifier, we’d suggest using the Port’s digital output – though we’d hesitate to suggest adding to the already significant cost by incorporating an outboard DAC.

I’m pretty sure I’m not getting influenced by what I read since I didn’t start reading until after I noticed the degradation of sound. 

And do a little research on burn-in.  I disagree that it’s psychological.  

I’m afraid I gave up on this kind of subjective stuff years ago, other than the fact that the words “cleaner and more detailed” suggest an improved THD+N, which is what one would hope for.

I do not continue conversations with people that take What HiFi seriously.

Given that publication’s apparent enthusiasm for MQA I have to agree.

I think it’s best that this thread be closed.  This has been most unhelpful and now appears to be devolving into something worse.  It’s clear that I must be completely wrong in thinking the Port’s sound isn’t as good as the Connect.  It couldn’t possibly true.  Clearly, I’m being influence by something I read.   

Thread closed upon request from OP.

The “burn-in” discussions that I read are flawed because there is more to this discussion than simply the number of operating hours post production. On most electronics production lines there is an operational test sequence spanning many hours. This should satisfy any “burn-in” considerations (if any) before the unit is approved for shipment.

I recall an older electrostatic speaker that needed about 72 hours for the membranes to fully charge -- every time the unit was powered-up. Best practice for this thing was to purchase on a Friday, power-up, don’t listen, then leave for the weekend. On Monday it will sound as expected -- then don’t power down. To me this is not “burn-in”. A “burn-in” would be a one time event. I’ve seen other high end units that looked like they were thrown together by a teen who knew nothing about design and physical construction best practices. These components are extremely temperature sensitive, required many hours to stabilize after power-up and didn’t react well to temperature change.  (I’m speaking as a former teen builder who noticed better results from the same circuit as I learned more best practice details) Some high end speakers are packed with a graph showing their frequency response. If this speaker requires “burn-in” by the user, how could this graph be valid proof of performance -- unless perhaps this is a performance comparison to a pre “burn-in” lab sample that later proved to exhibit the desired post “burn-in” performance. At best this would be a production quality control test, not a proof of final (post “burn-in”) performance.