What Plinius 250 are you buying? Is it the MK IV? If it is not then I could not help you much since I have never auditioned one. If it is a MK IV though I can tell you that I have done A LOT of research and I auditioned various amps before I settled with the Plinius 250 MK IV which is an altogether different animal compared to earlier series. To put it simply, the Plinius is the best amp I have heard in my system and in friends' systems and dealers in my audiophile life. And this even with much better speakers than mine. It is defientely better than (price) comparable Krells in overall finesse, musicality, detail and there is really not much of a comparison to Thresholds or Brystons or Classes out there. I have been listening to most of these amps in every occasion I could get and I can tell you the satisfaction I now derive from this baby is beyond description. It really breathed new life into my speakers.
GO FOR IT and you will not regret it. By the way, is it a new unit or a used one? There are a few great deals in Audiogon on 250 MK IV and I am amazed they have not been sold already!
I have also heard the Revels (dealer only a few miles from my house in Fort Lauderdale FL) and I love them. To these ears though they are a bit excessive in the highs a problem that the Plinius will take care of much better than your Krell ever had. It will infuse detail, delicacy and finesse in the system w/o taking away the "air" and transparency in the mids and highs!
Please, respond to me with your firts impressions when you get the unit! Take care and enjoy the music.