Seems like people that can't afford Krell love to stomp it without even caring to see further where the bad sound comes from. OTOH, Krell owners can also feel pressed to 'justify' their purchases since Krell products, even used, are so expensive. But the same can also be said about some of us that buy 'best bang for the buck' product. We'd like to think that we are smarter than those people that can afford to and do buy big-buck gears by saying that our 'cheap' system can come close or stomp a much more expensive system.
IMHO, the newer Krell amps are more like a transparent magnifier, so the quality of the components upstream is very important. I think that's the caveat with all the big-buck, hi-end SS amps, they are so transparent that you hear all the beauty and all the garbage from your source and pre-amp and you can't help but buy CDP/'table, pre-amp, IC's in the same class.
And the NAD, being more 'budget-conscious', I believe, is not as transparent as the Krell and therefore the better sound may be caused by its coloration that somehow complements the kind of sound that's coming from the CDP and pre-amp and makes it more musical. I believe if you are using a Krell amp (and pre-amp as stated in the original posting), you shouldn't use an Adcom as your CDP. It is better to use a Krell CDP and an Adcom amp.
It's not a matter of better and worse, just your preference.