Hi Millimeter,
I've changed tubes over time, from the original and new tubes in both preamp and poweramps to EI ecc83 in the preamp and Telefunken smooth plate ecc83,'s in the poweramp, together with KT88 (I didn't have any problem with my poweramps before switching the preamp).
The best sound actually comes from my fm tuner, not from my cdplayer of recorddeck. Changing tubes from stock to NOS improved the overall sound but it still sounds worse than the previous JP30 / JA30.