40sqm 2* Sonos 1 / 2 * Sonos 3 or 1 * Sonos 5

Save money to add a Sub once you have saved enough for it - that will take the set up into audiophile class. It will add richness to the music without troubling the neighbours - until the time you change your mind about that, when it will serve just as well!
Ahem, Sonos is far from audiophile class. ;)

However, if you have neighbors, you want less bass, as that's what penetrates walls if they're not fully insulated. Drywall very effectively reflects highs and absorbs many mids. Play 1 or Play 3 - I suggest the 3, since its better low frequency will make it so you don't feel you need a sub. I'm actually a really big fan of the Play 3, it's a nice middle ground speaker that gives you more punch than the 1's that everybody loves for their price, but gives you a decent mid to low end, without the bulk and expense of the Play 5's.

Save money to add a Sub once you have saved enough for it - that will take the set up into audiophile class. It will add richness to the music without troubling the neighbours - until the time you change your mind about that, when it will serve just as well!
Ahem, Sonos is far from audiophile class. ;)

Why? I have used audiophile - read expensive, which the only working definition I know for the word - kit for ten years, and Sonos sounds as good as the best I have heard that cost me USD 15k.
Going completely off topic:

Price has little to do with something being audiophile class. Take for example Blue Jeans Cables - compared to the names you've heard of, they don't sell snake oil and just sell good high quality cables, using science. Clearly audiophile class, yet not the most expensive by a long shot. Take a look if you get a second, I also love that they custom make cables to any arbitrary length (do know how much cleaner that makes a rack?). Instead, audiophile simply means, "someone who is enthusiastic about high-fidelity sound reproduction," and high-fidelity means, "the reproduction of an effect (such as sound or an image) that is very faithful to the original." (Merriam-Webster)

The first problem with Sonos is that the source material maxes out at CD quality, and even then only if you're very careful about bringing it into the system - let alone something like HD audio. CDs can be excellent quality, but most are mastered very poorly, as is the mass market digital music that Sonos understands. The second is that the Sonos DACs and processing change the music artificially - not always badly, but it's something you can't turn off, especially with their speakers - yet still, quite the opposite of being faithful to the original

My biggest speakers didn't cost nearly 15k (even the entire room didn't cost that much - and that includes TV, furniture, cabling, and such) and handily outperforms Sonos setups for accuracy and clarity. Even fed from a Sonos connect ALAC versus a pretty cheap ($150? it's been a while) CD player, using their own DACs, there's a big difference in detail and clarity that even my wife can notice, and when you've been trained to listen, it's a huge difference.

I'd put Sonos as more Bose-class - they use science to make you psychologically think what you're listening to is better than it really is. In many ways, that's more cool than being audiophile class' gear obsession with getting accurate sound, but they're distinctly different.

when you've been trained to listen, it's a huge difference.

I never argue with people that either are born with or have developed golden ears. Mine aren't.
Mine are far from, "Golden," but I consider them, "Good enough." :)

I've known some people with truly golden ears and perfect pitch, it's incredible what they can discern.

Yeah, Sonos with an ALAC CD rip versus a CD player wasn't so subtle. The Sonos connect put so much extra punch into the mid-bass that it affected the voltage on the circuit, and a measureable difference in current draw. Both set to 75 dbc on pink noise, going to the same receiver input, measured 2 dba apart peak sound pressure. The Sony CD player over POF TOSLINK versus using its internal DAC was indistinguishable to me (I'm sure they're all measurably different on an o-scope, but I couldn't tell), while the Connect got closer to true life (and a lower SPL) by using its outboard DAC.

Tried a second Connect, same result, so I fixed the curve as best I could in my matrix switcher - Sonos never gets used in that room anyway, but that room does have the audio matrix switcher as an input, so I verify everything in the event we have a party or similar.

I've met exactly two people with golden ears who had perfect pitch - they could reliably determine the difference between bitrates of MP3s, and one could tell which encoder was used better than chance. One musician, one mixing technician (the mixing tech could tell encoders). They didn't use super expensive gear, either, as working professionals they had good, but not great equipment. Lots of people with proclaimed golden ears, whose systems sounded amazing and were very enjoyable (one with solid silver cables, because why not?), but honestly to me it sounded like they just had better room treatment than I did.

Was 'Loudness' enabled, by any chance?
I would assume that anyone that has any insights into the subject of comparative testing would know that its validity needs a foundation of as close as possible to "apples to apples" bases for the subjects of the comparison. Along with knowing the necessity in listening tests for matching sound levels for both to within 0.2 dB of each other, an accuracy that cannot be achieved without instruments. Failing which, golden ears take over.