Idk about the BK, but the BH is quite a lovely match for the WS99. Really opens up the sound and is an awesome super portable amp with crazy battery life. I have to say that the E12 isn't so bad, either, though, if you're going for a really bass heavy sound. Lately I've been listening to almost exclusively trance and progressive and the WS99 with the E12 bass boost is pretty heavenly. The BH/BK would lend itself to a more well rounded listening experience, though.