IMO "String Quartet" is not a silly constraint. I take it to mean that the OP is interested in speakers that do an excellent job with small-scale, intimate arrangements emphasizing the mids. He isn't so interested in deep bass, a super wide sound stage, or the wide dynamic swings you get in orchestral music.
I had a pair of Totem Arros that worked very well within those constraints, in a small to mid-sized room. The speakers disappeared, the center image was very clear, the mid range was beautiful. The price was under $2K.