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