i am looking to replace my Krell with tube amps,

You don't mention impedance curve, which can be as important as sensitivity. If you want maximum sound levels in a room that size it will be hard to find any tube amp that will give it to you. Part of the equation of sound level is reflected sound waves and they will not know what part of the room you are using if the whole room is open. I don't know you feel about near field listening but in a room that size it might be your best alternative with tubes if you like loud levels.

Take a look at VTL, they have tube amps going up to at least 750 watts/channel. Havent heard any VTL in years so I cant give you any help there but in the past they've always sounded excellent.

What sonic changes are you hoping to achieve?
I really like the combination of a great tube preamp with a solid state power amp. I get what I feel is tube magic with a solid foundation. Is there just something about the Krell you don't like?

I'm with Rgs92, try a nice tube preamp in front of the Krells.