I had Class D for about 6 months (Bel Canto), liked initially but just couldn't connect over time. Class D is more clinical to me and less musical. I wouldn't say it lowered the quality just different and less favorable to me. Some love Class D.
Agree with jafant audition as much as you can.
The Hegel H300 is a very nice match with the Sopra's, I use Vallhalla balanced from a Cocktail Audio X40 and speaker cables are Silnote Audio Posieidons. Actually a very simple set up.
The system noted sounded very good with my Joseph Audio RMXL 25's, but now sounds like a whole new system on all levels with the Sopra No. 2's. Couldn't be happier.