You might want to check out the PS Audio BHK Signature preamp. It is a hybrid preamp, with input triodes and MOSFET outputs, and I think it splits the sonic signature accordingly, which might just meet your requirements. You can roll tubes to great effect to voice your system, it does impart a nice taste of the tube magic, and it is strikingly transparent, without being "glary" or "over-defined". At its price point, I'm guessing that it is a tough act to beat in the right system. My 2 cents.
What are the more subtle sounding tube preamps?
I mean "subtle" as in relatively less tube saturation or color than your average tube-pre. Common sense tells me less tubes as in a single dual-triode, but in reality that may not be the case. I currently have my eye on a CJ Classic. Not sure if that will fit the bill. Any suggestions welcome.