Tube-pre and interconnect match for Krell FPB-300

After spending some time with my B&K Ref 30 and my Krell FPB-300, I feel like I may be missing some of the 2 channel material. I'm happy with the authority and control of the Krell so I thought I might upgrade the pre-amp. The equipment is also part of a home theater but I have other amplification if the experts on this site think I need to remove the Krell for a music-only rig. This is eventually going to be a total upgrade from source to speakers(as $ allows) so any recommendations would be appreciated for all system parts. I'm currently leaning toward used B&W Nautilus 801s/802s or similar for speakers(I can't afford any of this new!).

I'm particularly curious about how tube pre-amps, with which I have no experience, match with Krell amps and what interconnects would work well. I hear so much about how musical tubes are.
I would really appreciate comments from anyone who has had a fair amount of experience with Krell FPBs. I admit I have very little experience with all except my current equipment. Thanks so much in advance.
I am running N801s with FPB-650MCs. I would not use another amp. The FPB amps match very well with Nautilus speakers.

If you end up going with N801s, you must realize AND accept that they need power to make them right. My suggestion, should power not be where you want to spend you money, find another speaker. That said, the Krell amps work well, (FPB series, older are NOT the same) but so would Mccormack DNA-2 Deluxe. I had nice result from Audio Research tubed monos at normal to slightly above normal listening levels, but the N801/N802 like juice, need power to make them sing, and also decent levels of volume to get the most out of them.

Bottom line, keep the Krell if going Nautilus.

I have heard you cannot use a tube preamp with the Krell FPB-300, without opening the amp up and flipping a switch. I spoke with an engineer at Krell, who told me that this switch, when turned off, cuts out an integral part of the amplifier. I believe the switch is supposed to counteract dc voltage. I would call Krell before deciding on a preamp. Also, I have had much experience with the Krell - B&W matchup. There is a synergy between these two brands that is unbelievable. I agree with Dan, keep the Krell and get some Nautilus speakers.
Thanks so much for the advice, it is much appreciated.

BTW does anyone have experience with the Wadia CD products and direct connect(xlr) to Krell? Seems, in theory, like a very logical way to keep the signal clean but it's a 100 mi. drive to audition so I want to know if anyone has tried. Thanks again...very much.
Most tune preamps do not have the bandwidth of an SS amp, they act like a restricter plate. Get a truly balanced preamp like a BVaudio, or PS Audio PCA-2 (I own both), maybe a tube CD player, like the Xindak SCD-2.