I agree with others that you'll lose transparency with a preamp, even if it's a Chord preamp. My take on the situation is that if you're still wondering if things can sound better, either you listen to a lot of old recordings and want a warmer sound so you'll want more distortion from a tube preamp (which I doubt) or that you have a bass frequency peak that is impacting the performance of your system that is a result of your room (& speaker and seat positions). This is because I think the frequency response of your Vandersteen is pretty flat so any bass response issues would be coming from room acoustics. Obviously, buying more electronics is not going to solve a room acoustic issue.
From my perspective, there are two potential solutions. One is to pay a true expert to fix the problem, like Jim Smith from Get Better Sound, who offers a RoomPlay service which helps you setup your speakers in person. Unfortunately, I've met enough self-proclaimed experts who really don't know what they're doing so I would only trust Jim Smith based on online comments. Of course, this would involve potentially significantly re-arranging your furniture/speakers by Jim Smith.
Another solution, given you already have a full digital system with UltraRendu, DAVE as digital preamp, etc., is to buy a USB microphone like miniDSP UMIK-1 and then run Room EQ Wizard to figure out what bass frequency response issues you have. If you play music off something like Roon, you can program in specific parametric EQ to digitally remove the bass peaks. My experience is that you actually don't want to simply use the measurements REW generates and punch it into Roon (or other software) because the music would lose a bit of life. And you definitely don't want to use the full room correction feature which I my opinion tend to over DSP the system. I generally just run parametric EQ on 1-3 bass peaks only and be done with it.
Theoretically, you can do both for optimal benefits. But my take is that given your system, if you're trying to squeeze even more performance out of it, it's good to go back to basics and fix any major bass response issues (in addition to other room acoustics issues, if possible).