Need insight on these amps

What amp did you have? What are you looking to improve upon?  What amp and overall sound characteristics of a system are most important to you?  Without this info we’re just throwing darts in the dark. 

I'm going to go out on a limb and suggest a Luxman as a counter point, or Ayre.

I think you should audition them if you can. Both will drive those speakers very well, add a lot of liquidity, with different overall characteristics though.

I owned the FPB-300 for about 20 years. I thought it was one of the better amps that Krell had produced SQ-wise, at least with the right system combination. But it does suffer from long term reliability problems. After about 13 years, I started to get distortion and had to send it to be recapped. It started acting up again after another 7 years and the expected bill to get it fixed wasn't worth it. I found someone to buy it for parts for more than I could sell it in fixed condition given the repair costs. I'd be pretty leary about buying another one of this generation. 

Hi audiogabby,
The VK-500 I had was opted out to the max as well. The difference between the 200 and 500 was extraordinary but so was the price. And yes, my 500 came from the early 2000s and I have to wonder if Viktor's stuff is still the same. I certainly understand about the ability not to be able to demo. It seems with the advent of the internet there is a lot of gear for sale but not much ability to "try before you buy". What type of load does the speaker you wish to buy present? The reason I had the Krell was to drive a pair of Apogee Stages way back in the day. Interesting story is that I actually drove the Stages with some tube amps. Jason Bloom the former owner of Apogee learned of this and he actually called me to tell me it could not be done. I played for him over the phone the amps playing the speakers (no Youtube or text messaging in those days) and he was astonished. He had promised to see this the next time he was in Seattle but sadly he passed before that happened. The reason for the story is this: some tube amps can drive some difficult loads; it is just not all that common but possible just in case you want to stay or go with tubes. Another choice might be some older McCormack amps, the DNA series. I used a pair of their monoblocks once and while not in the same league as the BAT or my large tube amps, they were pretty good once Steve "hot-rodded" them.
Thanks for the patience with my long answer.

soix, 
My last amp was a good amp but lacked transparency and therefore i felt the soundstage was not that well defined. I thought also about getting more power. They didn't feel like they were that powerful driving the Solos.