You can only add two surround speakers to a Sonos home theater setup. If you wire four speakers to the Amp, you will have two pairs of surround speakers that will be duplicating the same left/right surround audio.

You can add a second Amp to power the second pair of in-ceiling speakers so it acts as a separate zone and then group the speakers with Arc setup. But you will experience a slight audio delay from the grouped speakers when playing TV audio. Streaming music will be in sync though.

Thanks for the reply.

Are there any different speakers that I could use to get the main sound to the back of the room or do they all perform as surround?

No, unfortunately Sonos doesn’t provide a solution for repeating the ‘front’ data anywhere but up front in their Home Theater system.

You could, however, set up a speaker that is in a different Sonos ‘room’, and group the two ‘rooms’ together. That second ‘room’ would play the data from all the Home Theater speakers, albeit with a slight delay of 75ms. And that speaker could be placed anywhere you like. 

Thanks!

Sorry one last question. How many pairs of ceiling speakers can be hooked up to one amp?

I presume the Arc doesn’t need to be connected to the anp?

Depends on the ratings of the speakers. If they’re 8 ohm speakers, two pairs. Sonance makes some that can have up to 3 pairs, in their Architectural series. 

And you are correct, the Arc usually connects to the Amp across a ‘hidden’ 5Ghz network connection, so there are some distance considerations. Might be worth reading the wifi interference FAQ, just for informational purposes. 

To be clear, there is a single stereo  pair of speaker posts on a Sonos Amp, so no matter how many speakers you connect, they’d all be playing the same stuff.