Hi @rayrayray 

Welcome to the Sonos Community!

We do not recommend the use of in-ceiling speakers as surrounds as surrounds should be located at ear-level for the best effect.

So that leaves in-wall speakers - this would be entirely up to you, but the main disadvantage would be the cost. The current Australian price for an Amp plus 2 In-Wall Sonance speakers is $2,088 - significantly more than, say, a pair of Era 100s at $748, or even the more impressive Era 300 pair at $1,423. In addition, either Era pair would be easier to move to another location should you one day need to (if you rearrange the room, for example). 

In technical terms, the Era 300s would out-perform the In-Wall speakers when combined with the Arc as they also support Atmos audio - with 2x Era 300 added, your Arc system would become a 7.0.4 system (or 7.1.4 with a Sub).

Arguably, the only advantage the Amp and In-Wall speakers would give you is a cleaner look - if that’s your main concern, they probably can’t be out-done.

I hope this helps - if you have any further questions, please don’t hesitate.

Before buying any speaker that requires holes be cut in your apartment check your lease carefully, you could be facing hefty damage charges when you are ready to move elsewhere. Even higher charges if you want to take them with you leaving holes.

If nothing else get WRITTEN permission to install them.