With the Arc and Sub, the Era 300s as surrounds will give you a 7.1.4 home theater setup that includes side-firing drivers plus two extra upward-firing drivers from the surrounds to play height channel effects when playing Dolby Atmos audio. The in-ceiling speakers as surrounds will give you a 5.1.2 setup with no side-firing or extra upward-firing drivers from the surrounds. Because of the extra drivers on the Era 300s, you will get a wider and taller rear soundstage than the in-ceiling speakers.

The Era 300s will obviously be much easier to setup and take up more space in your room. The in-ceiling speakers will require cutting holes in the ceiling and running speaker wire through the walls/ceiling from the Amp to the speakers, but will give you a much cleaner look.

It would be helpful to provide us with more details about your room setup or post some photos.

which way sound’s better?

The Era 300s.

The living room is 23 ft wide and 9 ft high. what do you recommend?  thank you!

Get the Era 300s.

Get a Gen 3 Sub too, that room will really be better with one and maybe two, which is why you want the Gen 3.

If you do choose in ceiling speakers would you go with the Sonos 6.5 architectural speakers or possible the Sonance Mag8r which are 8 inches. Which would sound better in a larger room. Pros and cons? 

Using an Amps en Sonos speakers, the speakers can be Trueplayed, which will probablydo more for you sound than bigger drivers. The placement of in ceiling speakers (very high up) is however detrimental to your surround sound, and does not do Atmos. I’d go for the Era 300’s at ear hight.

thanks.