First of all the Krell integrated is NOT Class A, a pure Class A integrated costs much more to build than $2500!
Also the sound of the Krell in not particularly warm.
Class D is generally a type of amplifier which has a switching power supply and can be either a digital amplifier or an analog amplifier, the difference is weather the signal is converted to digital and then modulated or not.
As a Nuforce dealer, which are analog switching amplifier, the sound is excellent, and you should not rule out an amplifier because it is or is not a class A or switching amplifier.
It comes down to system matching and preference.