Amp or Port plus Hi Fi amp -- to connect to passive speakers

Not if you use the Port’s analog outputs. It’s a corner case issue with the digital output, if variable volume is used.

Another great amp:

https://www.rotel.com/en-apac/product/ra-1572mkii

I would buy the brand - between Yamaha/Sony/Marantz/Rotel - based on availability of in-country warranty and service because these are meant to be used for decades.

My daughter has my handed down Rotel that needed service this year to fix one channel loss after working flawlessly since 2003 when I bought it.

And there is no audible reason to NOT use these.

On that point: I know it sounds crazy to wire an Echo Dot into an amp like the linked Rotel, but only for psychological reasons, I have discovered.

@PennyP : Over the last two years, my annoyance at Sonos at their antics for promoting their future even if it meant that I have to trash my Sonos hardware that is in perfect working condition finds an expression in many threads, and these views immediately raise the ire of a handful of inveterate Sonos defenders on this site who think that Sonos can do no wrong. So, what follows is ironic, but true nonetheless.

A system consisting of a Sonos 5 pair, anchored by a Sonos Sub, properly set up and tuned, will not be far away from the sound you will get from the amp + Dynaudio system. For maybe half the price. And from the two 5 units, you will get two sets of line in jacks. One of which can even accommodate a Show 8.

Since the price will be less, a correspondingly lower service life should not be an issue. The only caveat is that you must have a robust local WiFi in place.

My suggestion therefore is: make sure you are ruling out this option for good reasons.

Thanks very much everyone for all the input -- I’ve learned a lot.

So coming back to the original question and summarising -- and setting aside, for now, the suggestion of trying out a pair of Sonos 5s plus the Sub: is it fair to say that if I’m happy to forego the ability to add more than one input device, the Amp would pair well enough with the Evoke 20s such that I can avoid the extra cost of getting both the Port plus a third party amp … with minimal or no compromise on sound quality?

I see Sonos states that the Amp will deliver 125 wpc into 8 ohms and 250 wpc into 4 ohms, which seems to meet the brief for these speakers.

Set up your Sonos Amp | Sonos   

Yes, but do remember sound quality is very personal, so I'd go somewhere to listen to to the Amp with the Dynaudio's to see if they are suited to each other. Different amps and speakers can sound differently. Trust your ears.

I have used many solid state amps in the past, and as long as they were not underpowered, they had no influence on sound quality. So, while I have not used the Sonos Amp - I have its predecessors, two Connect Amps - and I trust Sonos to not have screwed up on amp fundamentals.

But speakers, and especially how they will sound in a given room, is a major item because what you finally hear is the interaction of the speaker with the room. For an investment as high as those Dynaudios, I would play them extensively at home in the target location, with music you like, with any amp that is in the same power delivery leagues as the Sonos Amp if the Sonos Amp isn't at hand. Ideally having the amp will be good, but not essential. But listening to the speakers as suggested, is a must. Buy only thereafter. 

Note also to not skimp on speaker cable quality where conductor core thickness is concerned, such that it is adequate for the length of the cable run. It isn't necessary to buy the expensive HiFi branded and overpriced speaker cables, as long as this aspect is taken care of.