Hi

There are several questions that need be answered before anyone can advise you…

1. How many in-ceiling speakers are involved?
2. How will they be used...for ambient music, home theater or both?
3. You might want to read the information at this Link regarding the Amp

Thank you very much for the helpful questions!

1. How many in-ceiling speakers are involved?

1. Four pairs of KEF CI 160 mounted in B-Systm secoboxx

2. How will they be used...for ambient music, home theater or both?

1. I want to use it for ambient only. Besides, multifunction like doorbell, reminders... Selection of sounds and music by KNX rules (Gira X1)

3. You might want to read the information at this Link regarding the Amp

1. I have already taken a very close look at the latest Sonos amp. It would be suitable, possibly even overkill for the KEF CI 160 speakers I want to use. 

Hi 

I’m not familiar with KNX capabilities, so no comment on that front. I can comment on the use of the Sonos Amp(s) with your KEF CI 160 speakers.

1. Sonos Amp can handle up to 4 speakers at 8 ohms
2. It’s recommended when assigning 4 speakers to a single Amp to wire them in Parallel and not in Series
3. As the speakers are in-ceiling it's recommended to configure the Sonos Amp in Dual Mono Mode. Doing so ensures the listener hears the same sound no matter their position in the room.
4. In your scenario you have the option to have 4-zones (Sonos Amp x 2) or 2-zones (Sonos Amp x 4)
5. Using the Sonos Amp x 2 or 4 you can only play one genre to an individual Amp (Zone).
6. In 4-Zone setup (Sonos Amp x 2) you can play up to 4 genres.
7. In a 2-Zone setup (Sonos Amp x 4) you can play up to 2 genres.
8. You can group Zones to hear the same genre on all speakers
9. You can also group the Amps to a Sonos soundbar to send broadcast audio to the speakers.  There is a 75ms delay. Therefore, it’s not recommended when the Amp speakers are in the same zone or close proximity to the Sonos soundbar.
10. All Amps are Airplay2 compatible 
11. You can also connect a CD player and/or Turntable to an Amp via line-in. *

 * The turntable (TT) must be pre-amped via built-in or outboard between the TT and the Amp.

Hi AjTrek1

Thank you so much. 
If I got you right, I would need an individual amp for every speaker pair since any four are sitting in different rooms and sometimes need to play a unique program. 
If this is the case, it is a significant investment for the ceiling speakers, and I wonder if the older Sonos connect amp, which is currently heavily discounted, would be good enough.
Is there anything the new Sonos amp does what the older Sonos connect amps do not do?
I don’t need too much power for the KEF speakers and only need stereo, no Dolby Atmos or anything complicated. 

Hi @blue snowman 

The difference between Amp and Connect:Amp

Amp is more powerful than Connect:Amp, supporting 125 Watts per channel versus 55 Watts per channel. Amp also features an HDMI ARC input for TV integration, allows control with Apple AirPlay 2, and supports Trueplay when powering Sonos Architectural by Sonance. Both Amp and Connect:Amp have RCA line-in options.

AirPlay2 may be the most important feature in your situation as it allows you to send music stored on your iPhone directly to the Sonos Amp(s).

Just to be clear..If you have 4 speakers connected to a single Amp with 2 speakers in Room A and 2 speakers in Room B both rooms would be forced to play the same music/genre. The only way to have different music playing in both rooms would be to use two Amps...one for Room A and one for Room B.

Click the links for more comparison info on the Sonos Amp vs Connect:AMP

Sonos Amp Specs

Connect Amp Specs

I hope this clarifies things.