Thanks much for the long review; very informative ans interesting.
One comment about the huge Dynamics when needed by classical music. I also own the same, almost vintage now, Monbrison preamp. The 6x4 tube for power regulation needs to be changed every 1000/1500hrs. It costs really nothing, maybe just 20$...
So I would encourage to find a good NOS tube from Matt and make the replacement (if not done already). A tube 'guru' here in France recommended me the 6BX4 (strictly equivalent) from Mazda / Mazda-Belvu
