Well, I haven't heard the Classe's, but have heard the Krell 600 and it is an extraordinary power amp which has received superb critical reviews. Given the two amps you are considering, you do not appear to have a tight budget, but I'd suggest you also audition the Bryston 14B-ST, which has been getting outstanding critical reviews as a powerful yet sweet and refined power amp (it uses a new Motorola bi-polar output transistor that is said to have superlative audio qualities). The 14B-ST is essentially two 7B-ST monoblock amps on one chassis, but built with the improved Motorola output transistors, and rated conservatively at 500 watts per channel. For more info about the 14B-ST, check the Bryston home page for product reviews (www.bryston.ca). Also, HiFi+ magazine (British publication) has a review of the 14B-ST in its current issue.