I have not heard a direct comparison between the two (although I’ve heard both), and either would make a fine choice. The Oto is a terrific sounding amp that works well with any reasonably efficient speakers. Of course it works well with the AN-K.
i would expect a lot of other tube amps would sound fine too. I am partial to 6L6 or KT 66 amps. I particularly like the Synthesis A40 (60 wpc KT 66 amp), which comes with a good built in DAC and remote control (a big plus to me).