The Threshold 4000 is the last in line of the Stasis series. The amp was designed by Nelson Pass one of the great audio designers. It's rated at 200wpc in pure Class A. As a mono block it will go to 700wpc. In todays market a 200wpc class A amp would cost you $15-$20000. I have a pair of modified Threshold T-50's the run at 100wpc in class a and they run my Aerial model 6's without breaking a sweat. Being they are class a they will run very hot so the best way to run this amp is on an open amp stand don't put it in a closed rack it needs air. If you have a problem w/the amp contact Jon Soderberg at Vintage Audio. He worked w/Nelson Pass during the Threshold years and is the foremost expert on these amps. During the past years I've demoed Audio Research, McIntosh, Cary, Parasound Halo etc. and could never find an amp that could top my Thresholds. By the way check out Nelson Pass on line an intresting history.