Whatever choice you make get a truly differential balanced preamp. The Ayre gear is meant to be run with a balanced signal and although it sounds okay single-ended balanced is the way to go. The mere presence of XLR outputs on the preamp does not necessarily imply a balanced signal. Atma-Sphere, Audio Research and BAT are balanced and I believe Aesthetix is too. CAT, ModWright, Herron and (most- perhaps all) VTL are single-ended.
Ultimately there are better preamps than the K-5xe or K-3x but within their price range I haven't heard a preamp that is absolutely better. The affordable tube preamps are more different than better in any absolute sense.
Ultimately there are better preamps than the K-5xe or K-3x but within their price range I haven't heard a preamp that is absolutely better. The affordable tube preamps are more different than better in any absolute sense.