Leben CS600 required tubes

i own Leben CS600 integerated amp,which can accomodate 350B,KT66-77-88 and 6L6Gc,which tube sounds best to provide delicate ,resolving and relaxed sound

I would suggest Tesla NOS EL34s as another option.

I agree regarding the 6P3SE; a bit too forward.

Of the 6L6 world, I recommend GE NOS

Another vote for KT66 though I've not heard the 350B. I also like the KT77 by Gold Lion not personally a fan of KT-88 or higher.