A couple of years ago I replaced my Krell MDA-300's with a pair of Solo 575's. I first auditioned the Duo 300 in my home driving current Legacy Focus SE speakers. The Duo 300 had nice midrange and high but didn't have the bass slam of the older mono amps. Krell and my dealer arranged for me to try the Solo 575's in my home. They sounded great from day 1 and still do. I am still using my old KRC-3 preamp and see no reason to change.
I am waiting for a date to bring the amps to Krell for the upgrade. I don't expect any dramatic sonic improvement but willing to give the upgrade
a try. The lower output impedance should work well with the Legacy speakers.
As for the fans... I have never heard them. Aesthetics??? Are you kidding? Large power amps never look like fine furniture. These are understated and don't stand out in the room.
I may post my impressions after the amps are upgraded.