A couple of recommendations in isolation (i.e. I do not know if these preamps play well w/ Krell electronics) are:
Audio Research SP-6A or B or C, SP-10 mk2, SP-11
Kora Equinoxe
FWIW. YMMV. IMHO.
Audio Research SP-6A or B or C, SP-10 mk2, SP-11
Kora Equinoxe
FWIW. YMMV. IMHO.