To have a warm sound firstly there has to be warmth in the recording. Otherwise any warmth imparted will sound artificial. Secondly, the rest of your kit needs to be able to impart the original warmth, especially your headphones. If your headphones are not capable of producing a warm sound you won't hear one. The belief that modern tube amps produce a warm and cuddly sound like grandpa's 1950's radio is a myth. Finally, as a group, 9 pin Noval tubes like ECC88/6DJ8 tubes that we regularly use in Vali2, are not particularly warm and euphonic, Many were never intended for audio equipment, rather for scientific and military use. They can sound very good, but not often with a warm glow. For that warmer, embracing euphony for me Octals are required, such as 6SN7 tubes. They need an adapter and a socket saver to use with vali2 and there's quite a lot of discussion in the threads about them and how they sound. Of course we all hear music differently and this is just my personal experience.