How do you plan to use this system? You posted in the home theatre section so I presume it will be used mostly for TV/movies, but is that the case? What is the room like (option for full surround setup, closed or open concept, large or small, in an apartment with shared walls or somewhere you can crank it up without the cops being called, etc)?
Do you also plan to also use it for just music from time to time?...if so, how often and would it be more for background music, to listen critically while focusing on or getting lost in the music, to play loudly at parties, etc?
If home theatre is your main usage, and the room allows for it, I’d recommend expanding to a 5.1 system. That means adding a center channel, surrounds, and a subwoofer. You’ll find a surround setup far more immersive than just stereo, but it’s not the right call for every room. The center channel would ideally be matched to your towers or at least as close to them as you can get for your space and budget...B&W’s current 600 series is another $600, so it may or may not be worth looking at previous years’ models or something that isn’t a perfect match to free up money elsewhere if your budget isn’t flexible. Given your budget, I’d definitely save money on surrounds and get something cheaper than the current b&w lineup...consider used here too. I have built-in surrounds in our main family room to minimize the footprint, but that’s only an option if you own the home and can run the wires...it’s worth considering if aesthetics matter in your space though. You can often find open box in-wall speakers really cheap since they don’t include a speaker cabinet.
I agree with the subwoofers recommended above and have a SVS myself. The feel-it-in-your-chest sensation of those deep bass tones adds a lot of impact even vs large tower speakers. If not the swiveling your head around to look when you hear something behind you from the surrounds, the subwoofer provides the most “wow” moments for people new to good home theatre.
I also agree that at this stage you shouldn’t spend much at all on cables. The sonic improvement of expensive cabling over cheap cabling is tiny compared to the benefits you can gain elsewhere at this point.
This is just one idea. Expanding to 5.1 will make TV & movies more enjoyable, but if you don’t have the space for a surround setup or are interested in streaming, more time focusing on music, or want to get into vinyl then your money can definitely be better spent elsewhere. $1200 could get you a lot of great options but it really depends what your goals for the system are.