my 2 pennies worth-
had a denon amp- upgraded to a hafler- huge improvement.
replaced the hafler with a m.levinson 23.5- huge improvement.
replaced the 23.5 with a KRELL fpb-300-much better soundstage
replaced the krell with rowland m12 monoblocks-more refined, with a more realistic presentation of vocal recordings.
replaced the rowlands with levinson 33h monoblocks- another significant improvement- dynamic, musical, very quiet background ("black"). don't ask me how/why i did all this switching around; let it suffice to say that the krell amp was a worthy successor to the ml-23.5, but not the last word as compared to pass aleph 1.2's or the rowlands. i'm quite sure there's something better than the 33h's, but for now they sound astonishingly good-they really suprise me every time i sit down to listen to music. heard halcro's, and was impressed but not inspired. there are of course boulder, mbl, and goldmund amps in the $50k range that are probably "adequate"(!)-who knows. what i don't like is that krell seems to re-design its equipment with every new moon or so. sticking with a classic design with changes INSIDE the box make more sense to me. i thought the fpb amp looked great just the way it was. and this insane upping of the power ratings (600wpc, 650, 700, etc) when all you really need is 100w of clean, musical power, always there when you need it is almost always adequate, unless you throw alot of parties...the main object imho is combining musicality with very low noise. and as for the newest m.levinson amps, they may look wimpy compared to a 336, but stereophile reviews fwiw give them high marks in both areas.