I went up the Krell line of amplifiers in the 1990s, and ended with a FPB 600, which deserves high praise, but has certain - let me say - conditions. In my system, it sounded much better when it 1) got a dedicated power line, 2) a solid slab of stone below, 3) a good tube preamp rather than a mid-line Krell or other solid state (the manual warns of possible problems with a tube preamp, a jumper can be used, but I noticed much better sound without it, and never had problems), 4) using balanced inputs, and 5) matching speakers. The ones I had (Dynaudio Consequence) were a bit too much even for the 600. So the sound went from good to marvellous only on a quite high volume level (the amp shifting into class A operation). Even this power beast could not really unsettle the rather Germanic Dynaudios and make them sing and dance. Experimenting a little with speakers, I marvelled at how good the amp could sound driving an easier load. Since it was not possible to add another 600 amp to my setup, I ended selling both the amp and the Dynaudios, and bought Atma-sphere MA-1s instead.
I could say "I have never looked back", which is mostly true, but having lived with the Krell for ten years I have a lot of respect for it, it is a classic in some ways, and I have often wondered if there was even more potential to it than I managed to exploit in my setup. It is a bit of a paradox, the FPB 600 was sort of a "solve-all" when it came, it should not matter what speakers you gave it, it ate them all, and so on - but my experience was different, this amp is so good that everything you do - in terms of speaker matching, and the points mentioned above - is well worth it. Just before I sold it I had the Krell drive my small Aurum Cantus 3 speakers to great heights.
