I have an active crossover on mine with a 300w amp pushing a 10" subwoofer in a sealed box. It's an amazingly musical combination, the bass is very tight and the SSK-30s handle everything else perfectly. The active crossover is between the pre-amp and amp so that the (Marantz) amp can dedicate all of it's energy to just driving the 30s and they don't even have to try to reproduce the very deep lows. I can set the crossover to 70, 90 or 120Hz but mostly just leave it on 120Hz. I wouldn't swap it for any other speaker system.
I just got a pair of these off of Ebay. They sound amazing . Great resolution and with the right amp and a sub ae extended and tight in the bass region . Very smooth with the Carver Sunfire amp
I've found a video of a guy pairing SU-C3000 preamp w tube amp ( Sansui ). Also sounds amazing. SE-A2000 is nice but keep in mind that Japan model is a bit different than ROW one.