When I added tubes to my Krell 200 FPB/Adcom 750 pre, I started with a CAL Alpha tubed DA processor. Like you I asked here before making a move. I liked what the tubes added so much that I added a Cary AE-3 tube line level pre. My reasons for going with cary were the good comments/reviews here and the resale was good if it turned out to be a bad match. I called Krell, they faxed the instructions and said if it looked to hard just call back and a tech support person would walk me though the steps. I never had to call back.
If you would like to talk in person email me and I will send you my phone number.
Allan