You can’t bond the amp with your Play:5 speakers to form a single Sonos room, the way your 2 play:5 speakers are bonded as a stereo pair.  However, you can group the play:5 and your amp to play the same audio simultaneously.  It’s not any dfferent than when you play music on your play:5s and Beam grouped together, accept your amp+speakers+ play:5s would likely sound better.

Whether you consider grouping to be seamless is subjective I suppose. The only real constraint I can think of that adding two additional speakers isn’t necessarily going to sound better in the room.  4 speakers is not necessarily better than 2, particularly if the speakers are of different brands.  As well, your play:5 speakers can be trueplay tuned for the room, while the amp+speakers cannot.  If it were me, I would likely not put all 4 speakers in the same room, but setup two rooms each with 2 speakers.

Thanks for the explanation. Think you are right about 2 speakers per room. This would be my preferred setup: AMP + 2 Dynaudio speakers (and Sonos Beamer which I won’t group but only use for TV or airplay) in the living room. 

2 x Play 5 (stereo pair) in the kitchen. Problem there: as my router is in the Living room I cannot wire one of the Play 5 speakers to it.. So how do I get a stable Play 5 connection? Thx

Depending on how good your WiFi is you may not need to wire anything to the router. Or you could wire the Amp if practical, or buy a Boost and wire that.

My Wifi Network is actually quite OK. Strong signal & wide coverage and stable. Yet I have experienced without a wired Play 5, loss of signal. Not going to buy a Boost. 

You could wire your Beam or Amp as an option.  Any of them will do if you can’t go with the true ‘wireless’ mode.  

Also wanted to point out that the Sonos Amp does airplay 2 as well.  You won’t need your Beam for that.  Really the Amp can play your TV audio without any delay using the same type of connection as the Beam.  The only reason to use the Beam instead of your Amp+ Speakers for TV is if you just like the sound of the Beam better for some reason.

If that “no delay” is indeed the case, I would be very surprised if the Beam wins against the Dynaudio speaker pair. The speaker separation possible in the latter case will significant enhance TV audio effects that move across the screen, while the phantom centre channel effect will still allow dialogues to sound like they are coming from the screen. And the Dynaudio sound quality will be at least as good as the Beam, and probably better. The only downside to this is that there is no way to make the dialogues relatively louder than sound effects - I end up using sub-titles for all movies to avoid having the effects too loud for the dialogues to be fully understood. Since I am used to these for movies in EU languages, it isn't a hardship for the English ones.

I would try this set up which would also be excellent for just music play - and better than the Beam for this - and see how it goes. That then releases the 5 pair and the Beam for other rooms - I suppose the Beam can also serve well as a standalone music player.

It would also be a pity to leave the Dynaudio floor standers unused, or to even sell them in that case. They are excellent speakers - but power hungry, like Dynaudios tend to be. I would hesitate to use the Connect Amp with them, but the new Amp should drive them well. And since they do excellent bass, for the TV use suggested above, they would do much better than the Beam on the bass delivery which is needed for most movie sound effects - you would not feel the lack of a sub with these, as you will with just a Beam for effect heavy movies.

Thanks! Yes the new AMP would be the proper option. Having seen all comments I’d probably prefer the following set-up:

• living room- Music streaming (airplay + sonos): AMP + Dynaudio speakers. Separately the Beam just for my TV. 
• kitchen- 2 x Play 5 

what I’d like though is grouping the living room AMP/ Dynaudio speakers with the Play 5 ones in the kitchen. Is that doable?

Yes, the grouping is doable and a standard Sonos feature.

If your room is set up in a way that allows the Dynaudios to be kept on either side of the TV screen, you can easily do comparative testing of what works better for TV; I would be very surprised to hear that the Beam comes out ahead here.

I certainly will test this option, yet I think the Dynaudio volume/power is just too loud for standard TV programms. On top of that I cannot place the speakers left/right from the TV

Well, the power is in your control via the volume level slider. But if the speakers cannot be placed where needed for TV/movies, then the Beam is the better option for sure.

The thing is- I tried it once - connecting the TV (through this headphone channel output) to my amplifier- and I didn’t like the sound at all. I realize this headphone connection is crappy so I’ll try the AMP /Dynaudio solution. How does the AMP connect to the TV (Samsung?). Wireless oder cable?

I have the earlier version, the Connect Amp, that connects via a RCA stereo cable from the TV audio out jacks. In case of the Amp there are more options that will work better, via HDMI and/or optical cable.

See:

https://www.sonos.com/support/en-us/sonos-user-guide/index.html#t=sonos-user-guide%2Famp%2Famp.htm

But all will be wired connections.