I think I like the LA4 and CODA #16 (or #8) combo the best. Though I only gave the Serene a short workout with the #16. The LA4 also works better with the #16 because it is so small, and I can hide away from the amp.
I have been thinking about of adding a tube preamp into the RCA inputs of my CODA #16, which has a nice switch on the front of the amp to flip between RCA and XLR inputs. So, 2 preamps hooked up at the same time are easy to manage.
I am going to check out the Trafomatic Reference Line One tube pre.