They're a fairly stable 8ohm load, so they actually don't need gobs of power. I've run my Rosas with tubes and SS; currently, they're making beautiful music with Cary 805 monos (not exactly a Krell).
The Rosas are very tansparent, so your issues may involve something beyond your amp/pre (ie, source, cabling, etc.)
The Rosas are very tansparent, so your issues may involve something beyond your amp/pre (ie, source, cabling, etc.)