I'm still tweaking mine and it just gets better and better. First I swapped a pair of Sonicaps for the Auricap output caps on the SRPP circuit. To me, the Sonicaps are more open and natural sounding than the Auricaps. Then I swapped out four resistors for Tantalum films that Doc recommended. The result--increased clarity and detail in the SRPP circuit. Finally, I switched in a pair of Blackgate VK 150mf/350V caps for the last two 100mf electrolytics in the PS circuit. They have about 250 hours on them now but I've noticed a definite tighter control over the bass and more overall detail. The 5B is really fun to play with and tweak and I still find myself switching back between the two active circuits depending on the music but overall I prefer the CF circuit.
I've also rolled a lot of tubes through the 6R7 output circuit but there are surprisingly little difference between them. Otherwise, I've stuck with the RCA 12SX7GT's elsewhere.
Give us a full report after it's burned in.