personally, I'd got for the 20s for music listening. I might be a bit old fashioned in my love for 2.0 music, but when I had 18s and 19, I didnt love the way music was reproduced.  Wasnt by any means bad at all, but just didn't quite seem right to my ears.

I once listened to 18+19 and 20, both, at a dealer. I preferred the sound of 18+19. That said, I would buy 20s, I think. They are simpler and take up less physical space and less gear is needed to run them (I.e., only the Transmitter 1 can provide bass management for the 18+19 combo, which then requires using WISA). I have a BL19 for sale if you’re in the US and interested. See the For Sale forum. Let us know what you choose, what you hear and what your thoughts are!

There's no substitute for listening yourself!  At a dealer (Hallandale race track, Florida) the 20s sounded more "balanced", but less "precise", pardon the silly audiophile terms.  If it's your only set, or you listen to douf-douf, maybe get the 20s.  Otherwise, add the 19, because your 18s are way more handsome than those little nuns.  Yes, beauty matters, because none of the speakers at the dealership (including 5s at that time), reproduced, e.g. the timbre of a trombone or a brass ensemble better than what I already had!  (I did succumb and buy a set of 18s later, at/for another location.)