With the Amp, you are better off connecting passive speakers for the front instead of grouping a set of 100s. You will get a 75ms delay that is unavoidable because of the processing that needs to happen within Sonos speakers.

I have heard of users connecting to 100s using bluetooth, but I am not sure if that is a good solution either. I have never done this, because I have always had a soundbar for my TV, so someone correct me if I'm wrong.

The way that Sonos recommends is to use the amp for fronts with passive speakers, the the 100s as surrounds and the Sub.

@HenrikM 

And be aware (because you mentioned eARC connection) that Sonos Amp just supports ARC (without e) and no atmos. You would be able to connect it to the tv eARC port anyway, but won’t get atmos support, just up to DD5.1/DTS. 

How do the 75 ms latency mentioned previously compare with latency in other setups with eg sonos soundbar (various kinds) and wireless speakers. 
would you say that one should under any circumstances expect a latency of this magnitude ?

br

@HenrikM

Using a Sonos home theater device like one of the soundbar models or the Sonos Amp won’t produce any delay/ latency to the video. You get lip sync audio because of digital input and minimized buffering. 
If we are speaking of latency/ delay you have to differ between a latency that is caused by AD converting (what is just the case if the analogue input of a Sonos device is used… that isn’t the case here) and a latency that ist caused by network transmission between the home theater device and grouped rooms. 
The home theater device won’t „wait“ for the grouped rooms like it does in music mode,  because video lip sync has got high priority. 
Therefore in tv mode there’s that delay to grouped rooms. 
But my experiences have shown that you can equalize that with another function called „tv dialogue synchronization“. Normally that is used in the rare case if video output is behind audio. You can use the function to let audio „wait“ and play nearly synced with grouped rooms. The delay to video imo isn’t remarkable. 
 

But… spending a lot of money on an Amp just to achieve that imo is a whole overkill. If using an Amp, I strongly recommend to use ist with passive cabled speakers in the front like @Pools-3015 already said. 

Thanks for all the info, that’s very helpful. 
 

br