Is Audio Research Mach II Ref II a good pre-amp?

Can anyone advise me whether an Audio Research Mach II Ref II a good match with the Krell FPB 600C amp? I like warm sound with a bit of bite.

Take a bite out of sound? You bet!!
With the krell I'd bet a BAT VK5i would be a better choice.

I own a Krell 600c and it really is a smooth amp with no bite. The Audio Research would work quite well with it but I think it is way overpriced. IMO the LS-25 is a better value and probably sounds just as good. It also allows you to set the gain yourself. This way you won't overdrive the inputs. I believe the Ref has 18db of gain which is an awful lot.
I have the Audio Research LS25 in my system with a Jeff Rowland SS amp. The Reference 11 Mark 11 has the same tube(6H30) and similar circuit boards as the REF 11 MK 11. The Ref uses 6 6H30 , 1 6L6 and 1 5AR4 tube while the LS25 uses only 2 6H30 tubes. The gain for the Ref is set at 18dB while you can set the gain for 18, 12, or 6 for the the LS25. This may or may not be a problem depending on your amp. In my system the LS25 was 90 percent of the Ref 11 at half the cost. Of course this is very subjective and system dependent. I really don't think you could go wrong with either of these preamp. Good luck.
How could you possibly go wrong with it? See the review by Valin in TAS.