I am a huge LTA fan and love my MicroZOTL Preamp. I did recently purchase a Backert Rhythm 1.3 for a second system. The Rhythm is clearly superior to the MZ Pre but at twice the price. I wish I could comment on the Rhumba but I have never heard them side by side. The MZ Pre is no slouch and it’s not going anywhere.
i use NOS 12SN7’s with adapters. This is compatible with the 12AU7 it comes with. The 12SN7’s say Mullard on them and I didn’t know Mullard ever made any 12SN7’s.