Yikes.You like it bright it bright.Not sure what cable you use but I'd try Cardas (tames mid "nasties").Might make everything tight given your taste.I like three things accurate bass,lush midrange,and bright top end.But Krell and Thiel is for some folks but to much for me.I sold krell through FPB (mainly with a forgiving speaker which did not benefit for tubes being B&W).But So I know amp (great grip on bass,nice highs but for the tube lover in me the mids were a bit metallic and "etched" and Thiel being bright accentuates this).I would go for FPB (same Krell A sound with slight difference).Can't make bogus claim to CAST tech but I sold Krell and do known pricing and hype.I also got a pair of Thiel 7's for a buddy and wish I had gotten 7.2 since outsourcing driver tech was good move on their part.Better speaker.Others will have to chime in on CAST.Then room size and how loud you want it.I have a KSA300S and it is only Krell in their history that went continuous into 1 ohm (for 2,400n wpc).Bigger room and louder music 600 right?All I can say is I installed a CS6 and older Krell with wires which aren't bright (MIT roll off highs and lows) and it still made my ears bleed.I'd go FPB 600 (they can suck it down-dedicated 20 amp lines in houses with no filtering sounded best to me)and cable match carefully.This might not be of much help but sold Krell al the time and know they can be bright.Which is sort of dichotomy since I like lush tube sound on mids but like a bright speaker (so my buddy's tell me.FPB is less $$$ delivers goods and cable match to your taste is my two cents for what it's worth.For hell of it it you might want to head to head Parasound JC1 400 wpc mono's on Thiel's.Not sue if this was waste of time but you did mention not wanting Krell pre so thought I'd throw it out their.
Cheers
Chazz