Dan D'Agostino Momentum with Tube Preamp Anyone?

Has anyone heard Dan's stereo amp or separates with a tube-based preamp, such as the BAT VK-53SE or Nagra Jazz? How does this compare to using Dan's own pre? Thanks.
I have tried D'Ag mono amps with VAC Sign Mk IIa as well as ARC 5SE. Then when I heard it with D'Ag pre, it sounded superior (to me).
Tduski, what were the differences between those three preamps.
What is your main source David?

Cheers George
I have used the Dag Stereo amp with the Coincident Statement preamp as well as the new Backert Labs Rhumba 1.2 Extreme.  Both were killer combos!  
I love flipping gear and have had numerous components in 30 years, but, I have no idea where to go after the Dag.  It is the strong point of the system, the anchor.  I have it hooked up to 96db Tannoy.  With Purist power and a tube preamp into the Dag, I just enjoy the music.  Terrific synergy and the Backert pre is pretty incredible.  I've rolled some 1950's Mullards into it and the music is just so right.  My Tannoy love the power on tap from the Dag, which seems to hold them in a vice.
So, yeah, tube preamps work well with the Momentum.