can anyone recommend tube amp for dartzeel preamp?

A McIntosh MC275 Mk IV or Mk V would be ideal -- especially since your speakers come "pre-biamped" so to speak.

I 2nd the McIntosh MC275. There's a MK V recently listed @ $2,800 that you could probably get for $2,600.

I have one and it sounds great and I've had no problems, plus you have access to excellent McIntosh customer support if you ever need it.

this month's Stereophile has an Audio Research integrated that they think very highly of which is priced reasonably; under $5k. OTOH it may not be quite 'tubey' enough to give you that 'change of pace' you desire.

as someone who has your same gear, i have had the same 'temptation' but have never actually scratched that itch. i was always stopped by the realization that unless i go for 'the high priced spread'....a set of used Lamm ML2.1's.....the loss of information compared to the NHB-108 would likely cause me to never actually use the Tube amp much. plus i use the Evolution BNC cables for the 'zeel' 50 ohm interface which make quite a difference too.

you might contact Ruggyboggie who has been using his darTZeel pre with tubed amps for awhile and recently added the NHB-108. the only thing is that he does not yet have the 'zeel' BNC cables so he's not yet in a position to say how the 108 with the BNC'c compares to the tube amp without them.

i still have the temptation to have a set of nice tube amps sitting there i can try when the urge strikes, but every time i get a bit of scratch it gets sucked into tt's, RTR's, or other higher priorities.