Owned a KRC-3, most likely the worst sounding preamp on the face of the earth. Had a KBL (with a KSA-150), simply outstanding. Loved Rowland, currently have a SPECTRAL DMC-20 series 2, words cannot describe.
Just a note: Changing to a solid-state preamp will not improve your warm-up time situation unless you leave it permanently on or it incorporates a stand-by mode. Fortunately, this is easy and common to do with SS pre's, since there aren't any tubes to wear out more quickly. But from a 'cold' start, the SS pre will actually take much longer to come up to 'best sound' operating condition than will a tube preamp.
Zaikesman, good point. In fact, my Classe CP-35 doesn't even have an on/off switch on either the unit or the remote -- it's on all the time. I have measured it, it uses about 7 watts continuously, about like a night light. I don't think the 47.5 has an on/off either, but I'm not positive.
I have listened to the 47.5 and really would like to have one, but I have not heard the other preamps you mention. I generally like the Classe sound (just ordered a CA-200 to go with my preamp), which I consider to be less fatiguing and more involving than other solid-state gear I have heard. Others consider it dark or imprecise -- there are quite a few threads here on the Classe sound if you do a search, it seems to be a "love it or hate it" thing.
Given that you are coming from a tube pre-amp, the Krell isn't a very likely candidate. You may find it harsh, especially paired with the Krell amp (I say this based on reputation rather than listening). The Classe is generally considered more tube-like than much SS gear especially the Krell (and this has been my experience when I personally compared the Classe to other non-Krell SS gear).
If possible, let your ears be the guide.
Folks here are also quite capable of suggesting other alternatives, perhaps you want to post a more general question about "tube-like pre-amps" assuming you are happy with the current sound. Some searching will turn up existing threads along those lines also.
Your Krell ksa-150 would work very well with a passive. I have a Ksa-250 and have gone with passive in my system, the ksa-150 would be even better match than mine. It will not need warm up and will really bring your system to life. I would check out placette passive or Bent Audio passive. I went with the Bent audio unit but the Placette would have been fine also as the will both take your Ksa-150 to a higher level than the active pre's you are thinking about can do. The Bent and Placette units are about the same price and you can get them with as many inputs and outputs as you need, I chose the Bent because I wanted balanced inputs and outputs and the price of the placette goes way up if you want balanced model. You can get remote on both units if you like. The Ksa-150 is not a harsh amp at all so I would not listen to Ehart, as he even states he only knows what he has read about krell amps and thats about what most people know (what they read).
I OWN THE 47.5 AND LOVE IT. I TRADED MY KRELL KRC-3 FOR IT.
THE KRELL WAS VERY HARSH AND 'IN YOUR FACE' TYPE OF SOUND.
IT ALSO COST $4350. THE CLASSE BLEW AWAY THE KRELL, AND AT
1/2 THE PRICE.
I HAVE BEEN LOOKING AT TUBE PRE-AMPS. I HAVE NOT DECIDED
TO DO THIS YET, BUT, IF I DO, I'LL LIST MY 47.5.
IT'S IN MINT CONDITION. I REALLY LIKE MY 47.5.