Had a C1 and D1 home demo about 3 weeks ago, truly an impressive 2 box system both from a built quality and very impressive sound quality. So much so I bought the D1.
As with every new component that is added to an existing systems, there will be inherent differences in the sound that one had never heard before...in this case, mids and highs are vastly improved - clarity, separation, focus, height and depth is more discernible. Can't say much about the base although it reached the lower frequencies better but sounded slightly boomy. The speakers was repositioned during the demo sessions, which was a pain as it has spikes on footers on marble floors. I think that the speaker position is not yet right and need tweaking.
Bryston BP26/MPS2 and three 14B SST, Audiomeca DAC and PMC MB2/XBD speakers completes the system.