I think it would be wrong to call the RKV completely neutral or transparent. Obviously the amp does have its own signature but its signature isn't a strong one and it's certainly not the murky syrupy flavor that a lot of you guys associate with tube equipment. (Ie: components designed to sound "tubey.")
The RKV is clean enough to give you largely whatever you put behind it. If the source is harsh, the RKV is capable of being harsh. If the source is smooth, the RKV is smooth.
I would also say that the tube output stage on my CD player is not designed to sound "tubey." I don't know how the Tjoeb Noeb sounds and whether other tube output stages have a certain sound signature in mind so maybe the bias has credibility. I only wanted to respond with a "toldyaso" to those who thought it was a really bad idea in general.
It's probably not a permanent pairing, anyway, though. If I ever manage to get a source in my bedroom, the RKV strikes me as the kind of amp I'd like to have back there. A little rolled off on top, huge soundstage, a little bit soft - very relaxing. I'm sure whatever source I end up with in my bedroom will not be of the same calibre as my main system and the RKV won't sound quite as good as it does there, but I think in general something a little more pristine and precise might be more appreciated for the system in which more critical listening is done. The Prehead is probably a better fit there, for now. But right now, until I can afford to pick up a bargain DVD player or something for the bedroom, I'll have the option of both in the main system. Overkill in the extreme.
(Sorry if this came across as bragging - just telling you guys what my thoughts are on it all.)