Then I decided to upgrade to separates and tried in my system a friend's Nord NC500 with the Rev C Sparkos small opamps. I liked what I heard and decided to keep Wyred 4 Sound as a preamp (bought the excellent STP-SE stage 2) and chose my 3rd class D amplifier to be an Apollon NC800SL, also based on a pair of Hypex NC500 modules, but with the larger Sparkos opamps. This current pair of separates cost me about 4.5k usd (preamp was 2nd hand), which is a steal. This pair is a giant killer and I think it would be very, very difficult to beat without spending some big money (tens of thousands).
The STI-500v2 integrated went to my brother's system by the way, so all class D amps are still in the family. :)