The Mullard CV4003 is my favorite flavor for that center driver tube. It is the one I listen to 90% of the time and I'm sure it will remain my favorite because i prefer that darker sound on most of my music.
I would also like to try the opposite end of the spectrum since there is one genre of music that I sometimes listen to where I would like to find the brightest tube for.
What tube brand and model would you recommend that will increase the volume of the frequencies above 10Khz ? I am not asking about frequency response. I'm asking about tonal quality and linearity. I'm looking for a non-linear response in which the very high frequencies are at a higher volume.