I well understand pretty well what you write in regards to the difference in Beolab and Beoplay speakers. There has never been any challenge at all to my ears in noticing the sound performance between a Beolab 9 vs Beolab 12-2; etc. Over the past year as I grow fonder of the multiroom experience, I have purchased a Beoplay A6, M5 and most recently a Beosound 2, and am contemplating a Beoplay A9. Frankly, none (even the Beousound 2) measures up to any of my Beolab active loudspeakers. However, I find the M5's bass response somewhat muffled and not nearly as crisp as that of both the A6 and Beosound 2. I purchased a Beolit 15 two years ago and use it as a portable device. I find that its bass is somewhat lacking, and yet yields an amazing performance for any type of music played in a loud mode. I have only listened to the S-3's in a B&O showroom, so I cannot give them an accurate assessment or compare them to the other Beoplay speakers. If I were going to advise on a purchase given all variables including room size, options for placement, portability; etc., I would spend the extra money for the Beoplay A6 which is my favorite. --- Hope that my answer clarifies just a bit. 

Mattias N wrote:

While the "ranking" of Beolab speakers is quite clear...

Well, of course the BL90s may sound better than the BS1, but will you install a pair of it in your 9m² kitchen ?

Mattias N wrote:

For those of you that have listened to other Beoplay speakers, how would you rank/rate a _pair_ of S3's vs. an M5, an A6 or possibly a Beolit 15?

It's a matter of taste, habits and usages. You're the best person to answer your question.