Krell primer?

I was hoping some folks could give me a primer on Krell amps. I’m in perpetual upgrade planning mode and have seen a number of Krell amps coming through A-Gon. I thought I’d ask for opinions. It seems that the FPB and KSA lines, which I gather are at least ten years old, are relatively reasonable in price and seem well respected. Can anyone comment on their sound? How much heat do they throw? Are there any ongoing maintenance issues with the older amps? I understand Krell still services their older gear, much the way McIntosh does.

Any comments would be useful. Thanks!