Personally, I'd put an active x-over like the Marchand or NHT (if you can find one) between the preamp and power amp. I'd also think about adding a digital room correction unit for the subs (SVS/Audyssey or Velodyne SMS-1) between the bass output from the active x-over and the line-input to the subwoofer.
BTW, I had a KSA 50s for years and it still ranks very high among my favorite SS power amps.
Marty
BTW, I had a KSA 50s for years and it still ranks very high among my favorite SS power amps.
Marty