I listen exclusively to classical music. I love large orchestral, chorale, and opera pieces. I also love sonatas, trios, quartets, etc. I like the large pieces to be "you are there", and the small pieces to be "they are here". Orchestral music benefits for better extension of both high and low frequencies, more clarity, more air, more transparency. Smaller pieces benefit from more harmonics, tonal color, and decay.
With the BAT Rex, I get both, and that is why I haven't serious thought about another preamp. There is a switch in the power module that allows you to go from the 6C45 (transparency and extension) to the 6H30 (harmonics and decay). I use 16 EAT Tube dampers, 2 HiFi gold fuses, 4 Reflektor 6H30 DR NOS tubes, and 2 Philips GZ34 from the 1960s. The rest are inexpensive Sovtek and generic Russian tubes.
With the BAT Rex, I get both, and that is why I haven't serious thought about another preamp. There is a switch in the power module that allows you to go from the 6C45 (transparency and extension) to the 6H30 (harmonics and decay). I use 16 EAT Tube dampers, 2 HiFi gold fuses, 4 Reflektor 6H30 DR NOS tubes, and 2 Philips GZ34 from the 1960s. The rest are inexpensive Sovtek and generic Russian tubes.