What speakers?
The Krell stuff works well together obviously. Still, I remember the Sim as being sweet on top, with perhaps a better midrange than the Krell. The Plinius is probably somewhere closer to the Sim, while the Krell is perhaps a bit "cooler" sounding in the midrange, and maybe a tad dryer on top? I could be wrong on this, as it's been a while.
I very much would like to here others opinions on these amps as well. Honesly, I forgot myself between Krell and Sim. The Plinis I haven't heard in a multi channel version.
Still, I know it will depend on your speakers a lot. Trying one would ultimately be MUCH MORE INFORMING for you, I'm certain...you can always sell if you don't like.
good luck