I have a FPB300c through which I have had an extended opportunity to compare an Ayre K5xe and a Calypso with standard tubes. I preferred and ended up buying a Calypso. The K5x sounded like a more refined (less harsh/more tube like) version of the Krell KRC-HR I had before but the Calypso was more musical, much warmer, and just drew you more into the music. Initially, I thought the soundstage of the Calypso was less wide than the KRC but this changed with better tubes.
Hope this helps.
Hope this helps.