The one with the 76 pre-amp schematic and the guy with the A5's in the room. You have to e-mail him for the schematic I believe but he is still active. The show a ppicture of the xover in the article and the parts are all exposed. Seems cheap enough to Bi-amp, I used to electronically bi-amp my old DIY Focals and it did sound more spacious and full. I also sometimes bi-amp my 811/806/421 corner set-up with an active xover and that does well also. I cross at 1200 hz.