Richard, I forgot to include the info that the B4 filters can be set to 1st, 2nd, 3rd, or 4th-order, which is of course 6, 12, 18, or 24dB/octave. Much more flexible than the Bryston x/o, which is regularly recommended and used with Maggies. The there are the x/o's from Marchand, who make custom boards to provide any x/o frequency and slope you desire. And, some of the Marchands are tubed!