As for a passive treatment of your room, you ought to let a skilled person do the job – he will need to see the room and do some measurement.
A room like what you describe, is basically bad for sound, for listening…especially if you want to have a specific listening position (“narrow beam speakers“).
Also you should consider that these treatment – done 100% – will have a heavy effect on the looks of the room.
When B&O developed the BL90’s (and later on the BL50’s), they took into account that a lot of their costumer have acoustically bad rooms! These 2 speakers have a built-in room compensation, that lets them adapt to the room, when set up – and both can be costumized for specific listening positions (in fact several positions).
You will not have to worry that the 90’er or the 50’s can fill your room with sound….in fact more than that.
For insight in how the BL90 works please have a look here
As for your other suggestions (“BL17s, BL3s, or BL18s strategically distributed across the room, combined with one or two BL19s“), you will need many to compete with the 90’s/50’s….and you will run into trouble finding the right placement of the BL19’s. Apart from that you will never be able to have a specific/optimized listening position. You will never have this “listening corner (5 x5 m) where I can listen to music while sitting” – it will (at best) be an even sound from all of the room.
Apart from this you should think of the need for connecting these many speakers – they will each need power cables and the powerlink cables. Not that this could not work – it will be a different experience and taste can not be discussed.
By the Way, which source/s do you intend to use?
I’d say a set of the 50’s or even the 90’s is the right choice for such a room – I am sure you can arrange a demo at home – at least for the 50’s – from a good B&O dealer.
Hope this helps a bit.
P.S.
This said – there would be another solution….the BS Theatre has similar capacities for Room Compensation and for creating different Listening Positions.
This soundbar from B&O can without any problems be used as a stereo/2 channel setup. You can connect multiple (Beolab) speakers here and have these play unified for 2 channel listening. You can connect some of the speakers, that you have mentioned, wirelessly….which makes it easier to place these and rearrange if needed (they still need a power cord, though).
The soundbar itself could be hidden away – if preferred. This would also provide several sources and a control with a B&O remote respectively with the Bang & Olufsen app.
Edit!
Seeing the post that came just before mine was finished . the BS Shape could be an excellent option too – however it will not give you the specific, optimal listening position, you have written about. The Shape is a terrific speaker setup to fill a room with sound.
MM
