The mini-Sub should do well in that room unless it has large openings to surrounding areas. I’d make the sub my first purchase since you do music as well as TV. If you are concerned go for the full sized Sub but I just can’t see two full Subs in that small room unless it is almost a full open plan.

Surrounds are a question, the 100s are going to match the Beam in sound level capabilities and I’d likely go that way. I have Play 1s and Ones as surrounds for my Arc and Beam and they are good enough.

The 300s I haven’t tried and I rarely see any Atmos content so I’m in no rush to upgrade. I’d see what folks that do use Atmos have to say before going the extra expense. Positioning the 300s is pretty critical (as is the Beam Gen 2) if you want Atmos to work, stick to the Sonos recommendations or be prepared for less than an optimal experience.

You didn’t ask about Sub location but you really need to try it in multiple positions. In a corner you’ll get the most bang but the coverage may be uneven. Centered on a wall will be more even, and don’t rule out laid flat under the couch. Try multiple spots and if possible TruePlay each. Mine is in a corner and my room is an odd shaped open plan, however the sound is great where I sit.

Thank you very much! Noted on the Sub placement. Turns out it’s a Beam Gen 1, so I’m now trying to ensure the 100s + mini-Sub will be compatible, and if so, we’ll prioritise getting the mini-Sub and follow up with 100s.

They are compatible.  The Era 300s require a Beam Gen 2.

Fantastic! Thanks so much. It looks like the Era 100 placement guidance from Sonos isn’t so strict, so we’ll assume they’ll do fine at each back corner of the room, unless anyone on the thread has a strong opinion about getting them closer to our sofa.