You don’t need both a Sonos Amp and a Sonos Soundbar, with two rear surrounds. The Soundbar and the Amp play the front 3 HT channels, so no point duplicating those ...and your TV is likely to output its audio through the HDMI-Arc/eARC port at different time to its optical port, thus causing an echo effect.

So you perhaps need to choose one, or the other, for the front speaker part of the HT setup.

What also has concerned me is you mentioned the Sonos Amp as being ‘old’ ..because the Amp is a new product, so if you are referring to a Sonos Connect:Amp then that cannot be used for a Sonos Home Theatre front-speaker setup, but it can be used for rear surrounds, but must be ‘wired’ to connect back to the main front player.

Hope that assists you in your purchase decision.

Hi. If it is old then I assume it is really a Connect:Amp?

I'm afraid you cannot have a setup like this. The Playbar plays the front three channels so you cannot have additional speakers at the front. But then you don't need them.

Also, to drive surround speakers the Connect:Amp requires a wired  connection. This does not apply to the current Sonos Amp. 

Ken beat me to it!

Its the connect amp! 

Sorry, my mistake…

What can I do with the Connect amp to realize a theater setup?

Or what purchase would you recommend? :-)

Have you got the Sonos One SL speakers already?

Yes.

I would swap the Connect:Amp for the new Sonos Amp and cable that to the TV using its HDMI-Arc port, if that’s available on your TV. (If not, then use an optical connection, but you ‘may’ need to buy the Sonos optical converter, as I think that may not come with the Amp, so perhaps check that before purchase - if you do choose that route). Then use the two One SL’s as surrounds.
 

Then either sell the old Connect:Amp (it sounds old), or perhaps use it elsewhere in the home, if you have another pair of passive speakers… note that you would likely be better off using the new HT setup with the (gold) Sonos S2 App - I presume you are presently using the old (black) S1 App at the moment… which you can continue use with the old Connect:Amp, but they won’t talk/group with each other. You can leave both on S1 so that they do talk/group with each other, but you may lose-out on some future ‘feature’ updates, but that’s a matter entirely for you.

Thank you for your information!!

Very clear :)

I'd advise you to keep the Connect:amp for music. Provided your TV has an HDMI-ARC connection I'd choose an Arc (or if your TV or room is small in size a Beam) to bond that with the One SL's for surround.

This separates music and homecinema, but seems the best solution, if an Amp would not fit your cabinet..