The last two weeks i had several pre-amps for comparing. For the last 5 years i have used the Dan D'Agostino pre-amp connected to the Alieno amplifier (last 2 years) , before that with the Momentum mono amps.
The waiting was for a matching pre-amp, Alieno worked on it for more than 3 years. The last few months i have tried some other competitors because it wasn't clear when the Alieno pre-amp would be ready and i sold the DD.
So i tried some. The one i was very suprised with and think it is undervalued is the TAD C600. It bettered the DD big time in allmost all aspects.
The one i was the most expecting from, also because of the very good TVC volume-control and tubes, was the Nagra HD pre-amp. I had it for one week and 2 days together with the Tad and the Alieno pre-amp. I very much liked the way of using and operating the Nagra HD.
But the sound was a completely other story, i tried a lot with different interlinks, XLR (no good combi) and SE. The tone is quiet good but short notes, i mean allmost no decay on notes against the Tad and Alieno. Sounstage-wise the difference was even greater, it all is just between the speakers, from tweeter till tweeter and a bit depht. The Tad makes that muchhhh wider, you have way beyond the speakers, allmost as good as the Alieno.
The Alieno against the Tad has better depht, you can walk through the sounstage. The difference in that with the Nagra HD and DD is very big.
Offcourse it's often a match and synergy thing but i wasn't prepared the Tad C600 did it so very well.