pweg,
Which Absolares you have, and what's the speaker you'll be using?
I haven't heard the Absolares in a familiar system, but in Munich, they get consistently good sound. I did notice they don't play "big" music, possibly because the tube amps won't handle that well with the Rockport speakers they use. But for simpler stuff, it's indeed very smooth and warm, with excellent detail.
What you'll gain with the darTZeel is possibly an extra layer of realism, that only headroom allows. Unless you're using very efficient speakers (100dB+), the darTZeel will just sound more real, simply because it'll present the attack of the notes like they really are, and will never constrict the dynamics.
As an example, you can ask Mike Lavigne (or read his excellent write ups in his thread), who did a similar darTZeel x SOTA tubes, and ended up sticking with his darTZeel.
Michael Fremer has had many a tube and solid state behemoth in his room, and AFAIK, he still keeps the 458s, given how amazing overall they are.
With the new 468 monos, I think it becomes a no-brainer. If you can manage it, go for it. Better yet, keep both sets and switch at will
cheers,
Alex