I have Zu Omen original version, with upgraded caps and resistors.
I used it with Dared 2a3, then with Larry Moore 300b. As somebody mentioned before tubes have gorgeous midrange but have difficulty producing controlled bass.
At the moment I am running Zu with my custom Abacus TPA3116 - midrange comparable to that of 2a3 with much better bass.
Building TPA3250 and 3255 amps to see if improvements is SQ could be made.
I used tube amps for years, but went class D as the future lies there, in my opinion. Besides, here in the South the tube amplifier is inconvenient in the summer
I use my own John Broskie's Aikido preamp as well as Aikido Phono preamp.