I am using an Altmann Attraction DAC and BYOB amp with an Avantgarde Trio. Four days ago I connected/bought a Promitheus Ref5 TVC with some options between the two with Acrolink Mexcel cables. After running this system for roughly 100 hours I can say that this TVC works perfectly well in this config. I can second Herman's statement that there is only the first few position of the volume pot which is really useable for more domestic volume, but this setup keeps all the best part of the now famous Altmann sound, the coherence, the inviting tone and the entertaining, engaging rhytmyc capability did not change to the worst, but I got better dynamics and more grip from my system, then the straight Altmann to Altmann connection.
I changed to the Altmann amp from a very expensive Audio Note (original Kondo) Kageki using it for more than 6 years, and could not been happier with the change. I own the Altmanns more than a year ago, got a chance to compare the amp to lots of other tube amps in my system, and it is quite strange that in my system only the DIY tube amp owners heard their design better than the Altmann, ordinary tube amp owners not :-).