I think the Krc3 is a great preamp....very neutral & not outdated (albeit no longer made). I am not familar with the Kav 280p, but do know the Krc3 was a significant steup from the kav 250p. I would look at the Krell kct if you are really looking to upgrade your preamp.
The bigger issue...I don't think the issue is with your pre preamp at all. I use to own the Kav series amp and think they have very pronounced lower & upper end. The upper end can be very fatiguing. If you want to stay in the Krell family, I would upgrade to one of their bigger amps or even their new kav 2250 amps. I believe the newer kav line has a more balanced upper-end. If not Krell, you have so many options out there.
I am not familar with the rest of your gear, so bear that in mind. I just wanted to comment since I think the Krc3 is a very good preamp.
The bigger issue...I don't think the issue is with your pre preamp at all. I use to own the Kav series amp and think they have very pronounced lower & upper end. The upper end can be very fatiguing. If you want to stay in the Krell family, I would upgrade to one of their bigger amps or even their new kav 2250 amps. I believe the newer kav line has a more balanced upper-end. If not Krell, you have so many options out there.
I am not familar with the rest of your gear, so bear that in mind. I just wanted to comment since I think the Krc3 is a very good preamp.