hi mariusz:
i have tried rca, sylvania, tunsol, ge, brimar, mullard and probably one or two other 6sn7s. without the treble attenuation, i don't want to listen to the preamp. i have varied power cords and interconnect cables as well.
it is not a vintage tube preamp. many of the older cj, audio research, cary slp 70, and other older preamps are more satisfying.
i definitely prefer my nobis proteus and audio not kits l3 line stage.
if you like a somewhat lean and analytical sound, then the mapletree is ok.