Not selling my BW's--hope to add to them.
I was concerned my center is not powerful enough?
I sit 14 feet away--the room is 15'X25"
You can use them as surrounds, but if you get new front left and right, you will need a matching center.
If I was looking in the current market, the Kef R3 are being discounted nicely and while not a floor standing it is a 3 way that measures and sounds very good (a substantial upgrade over your current floor standers). You could pick up a 3rd on the used market for the center or their current center would work too, just pushes you over budget a couple of hundred dollars.
You might consider another sub as well in the future, as the single you have isn't really enough for your room size.