tubes and rock and roll, good fit?

The number of tube amps that will drive your speakers properly are far outweighed by the number of solid state amps.

Keep in mind, the operative word is properly.

If this were my decision, I'd look for a better pair of solid state amps and forget the tube idea.

As always YMMV

What about a tubed preamp with SS amp?

Look for something powerful, quiet, and with a well-regarded phono stage.

Much easier to demo, and it may get you entirely to where you want to go.

For a tubed amp, think CAT and BAT, in addition to the VTL. There are literally just a handful of tubed amps with power and bass.

I've dabbled with the idea of moving to a tube amp in my system, but I have determined their is little or nothing to gain. I think my situation is analogous to yours regarding tube amps because I wouldn't even consider it if I did not think tubes amps could do R&R to the max and we both have speakers that are not inherently tube friendly due to less than optimal impedance specifications to match to a tube amp. Then there is the maintenance and reliability issue which might be exacerbated with many tube amps being asked to drive a load they are not designed to do.

I think tubes and SS are both equally capable of doing R&R to the max. You need to match the amp to speakers first however, as Tvad indicated first early on.

If you are tired of the Krell and want to change (nothing wrong with that) but stay with your current speakers, then moving to a tube amp may be risky and harder to accomplish properly for the reasons already mentioned. If you are prepared to perhaps change speakers later as well in order to get the optimal match to a tube amp for R&R, then more power to you.

Even if someone comes back and says that the vtl tube amp sounds great with your speakers for R&R, that does not assure that things are optimal or even that you will think the same.

Bottom line: if you want to stay with your speakers, I'd be looking towards a different SS amp if you must. If you are willing to risk possibly have to change speakers afterwards in order to get the best performance possible, then go ahead and find a good powerful tube amp that is designed to drive 4 ohm loads optimally. That is the thing that may prove difficult or perhaps even impossible. Specs may insdicate the ability to drive 4 ohms but is it the optimal configuration for that amp? For a top notch system like yours, this could matter, Most good SS amps should be inherently capable, so you will have many choices as Audiofeil indicated.

Consider how many rock musicians/bands use tube amps. Any other questions?

Of course they will work but as others stated, most important is the match with your speakers. I'm not a fan of Krell, but then I only owned their amps/pre once. They offer good bass control (again depending on speaker match) but don't offer enough communication of the musical emotion for my taste. YMMV. I did own VTL 300 monos for a number of years and found them to be a great middle ground with characteristics of both tube (emotion, warmth, dimensionality) and SS (bass control, detail, clarity).

Pryso, I think musicians/bands often use tube amps as a means of introducing distortion in a controlled manner which is easier achieved with tubes than SS.

Same is true with use of tubes in home audio gear, but the goals of the listener of a home system is generally to avoid certain distortions, not apply it, which is different. BOth tubes and SS can accomplish this if done properly, whereas tubes are much better suited for introducing distortion into an electric guitar, etc.