CLASS D

If it's a Box Woofer Klipsch. You NEED JUICE to move that Woofer. A flea bag Tube Amp is only good on the Horns. I ran Orchard Audio Ultra's on my Cornwall IV's with a Tube Preamp (BAT VK50-SE, Black Ice Audio F360, and my favourite Black Ice Audio Aries Headphone Amp/DAC/Preamp. 

Or an active sub with the high level hookups.

Buckeye Amps. You're welcome.

Another vote for AtmaSphere.

Bel Canto. John Stronczer has class D dialed in. The E1X integrated is all you need.