Given you may be looking to not add any more tube warmth to your current system I’d second the LTA MZ2 with the caveat you need to also get the upgraded power supply (LPS) option. The added benefit is that the MZ2 is also an excellent headphone amp, so if you rock ‘phones or may in the future this could be a huge bonus.
I’d also add the Backert Rhumba 1.3 as another very well-designed tube pre that plays it closer to the detailed/neutral end of the spectrum, and if you can find one used a Rhumba 1.3 Extreme would be even better still. Just another option for you.
Lastly, and coming from a little different perspective, you might consider the Bryston BP6 solid state preamp. What??? Why? Well, the BP6 is the proverbial straight wire with gain design and sounds as close to nothing at all as anything I’ve heard in my system along with providing a dead silent backdrop to the music.. It will pass through everything it’s fed without filtering or adding anything, but in doing so it lets you to hear things in the music that were previously masked and allows the soundstage to open up and expand with the apparent removal of gunk that was previously clouding the whole performance. I brought this up because as I look at your system and hear what you’re looking for, the BP6 could be like an audio enema for your system that allows it to open up and express itself more clearly and completely while maintaining all the existing tube goodness. Anyway, there it is FWIW, and best of luck in your search.
