Question on tube preamp

I have the Dynaudios C4 confidence Signature paired with Plinius Tautoro pream and Plinius SA Ref Power amp. I am thinking of buying a very good tube preamp for my system. Any suggestions?
A Conrad Johnson or BAT would be an improvement. Contact me if you are interested.
While my situation is not identical to yours gear-wise, it may be close enough to be somewhat meaningful.

For the last week and a half I've been enjoying a new-to-me used Symphonic Line "The Enlightenment" tubed pre-amp. It is currently feeding a Plinius SB-301 driving Revel Salon 2s. It was rebuilt soup to nuts within the past 18 months by an authorized SL technician using the same parts that go into the newly built units. So it is in essence a new unit sitting in a 1999 chassis.

The SL pre is replacing a Plinius M8 pre. The M8 provided strong weighty bass, good dynamics, dark background and a broad soundstage, and mated quite well with the SB-301. The SL pre is providing just as much bass weight with more detail, a plainly superior mid-range, and a far more detailed treble that at the same time is less fatiguing at higher volume. The SL pre also is plainly better in terms of micro-dynamics and depth of soundstage. I would characterize it as just slightly on the warm side of neutral, but not at all rolled off in the treble like some other tube pre-amps I've heard. Nor is it at all slow - this sucker is fast on the attack.

This is not to say that the M8 is a lousy pre-amp. It's actually a quite nice pre-amp and provides a very solid sound. But the SL pre is leagues better and frankly has showcased the SB-301's talents in a whole new light.*

Hope this is somewhat helpful, and good luck finding the improvement you seek!

*Alas, the SB-301 faces heavy competition this week from a pair of incoming Symphonic Line Kraft 250 monoblocks.
I used to have C4's driven by a Plinius SA-102 amp and Aesthetix Calypso preamp. IME, you can't go wrong with Aesthetix preamps. Good bang for the buck, dependable, great support and you can tailor the sound by rolling tubes.
Nagra PL-L
Doesn't the Plinius have a balanced input? If so, you can minimize the effects of the cable and the amp will perform better if the preamp is also balanced.

Just keep in mind that not all balanced tube preamps are equal. Some can't drive long interconnects, even though that is one reason you might go balanced. Others can't drive lower impedances often seen in transistor amplifiers (they start to loose bass!). But some can do all these things with no worries.

A fully differential preamp will have no 2nd order harmonic richness that is often associated with tubes. This can allow the preamp to be really neutral, highly detailed, yet also quite relaxed- a very nice combination!
The Plinius amp has a balanced input that I use with the Plinius pre, but the SL tube pre is single-ended only.
i have listened to a lot of preamps. in general i prefer older preamps, such as the audio research sp 10 and mcintosh c 22 ( old stuff). there is one exception. david berning's latest preamp is a great piece, if you have the bucks.

otherwise, if you want to stay reasonable, look for an older preamp, tubed , of course.