Ok, just in case anybody would be interested , here's the final results. It turned out to be VAC phi 200 power amp that caused all noise problems. Why - not entirely clear. Input impedance of VAC is 100 k, theoretically good match for Ayon.
Even more to this story, my Aesthetix Janus preamp ( which I thought was prone a bit to tube rush noise) turned out to be dead silent with... Yes, different power amp. Cary CAD 120 mark II. Tech specs almost the same.. Same input impedance. Same KT88, 6SN7 based power amp. But somehow Cary is absolutely quiet and VAC is not.