I have spent lots of time with the Solo 575 mono block amplifiers. They immediately sounded better than the EV403e I was running. Much larger soundstage, noticeably more speed (hits on a high-hat, fast guitar, etc.), even more tautness to the bass (even compared to EV900e mono amps), and they are just far less harsh than any of the EVO amps. They also run cool, and the fans are very quiet. There is one scenario where you can hear the fans, if you playing something at high volume, and then all of a sudden you hit pause, or the song abruptly stops, there is a ~1 sec, quick ramp down of the fans that you hear as a whoosh. It's never noticeable at any volume you are playing. And they are silent when you are in your listening position and they are idling. They only require 2 inches of clearance above them too. Most importantly they are the best sounding Krell's ever. I'm a Krell dealer, but I'm just as critical as I too am a user. iBias is a big step forward. Hope that helps.
PS I have a video/text of the EV402e vs Solo 575, same track, same volume, same everything. Even with an iPhone and it's crappy mic/speakers you can hear the difference clearly. Way better dynamics, transparency, everything with the Solo 575.