Your Playbar provides the 3 front channels and the Play:1’s add another 2, so that’s all five in a 5.x system. Currently(?) Sonos doesn’t offer an option for separate speakers up-front so you can’t add any more other than Sub to add the .1 to bring your system to 5.1. 
 

You can use the Amp to drive other speakers. They’ll be identified by a different room name but they can of course be in the same physical room. So you could have a pair of speakers for music and the home theatre kit for tv/movies.
 

They can then be grouped to play the same source. They’ll play in sync except for video source from the Playbar, which will give a 70msec delay which is an unavoidable aspect of how Sonos implements its multi-room capability. 

What are you using the Amp for? Are you using it to power a set of passive speakers?

Since you already are using a pair of Play:1s as surrounds, you cannot add anymore surround speakers to your Playbar setup. If you want to improve your home theater setup, consider adding a Sub.

Thanks for the info  

I will look to get a sub instead 

Cheers