Dear rauliregas
You ask "I think your PS is high gain active unit then why a SUT?"
Indeed. "Active" is just the beginning, regarding the Aesthetix Io, you could add dynamic, explosive when needed, and especially, pure. Pure tube sound all the way. If you like that kind of sound (I suggest we don't take that debate here).
There is only one caveat. You need a quite strong output cartridge. My Lyra Atlas works fine at 0.56 mV. If it goes lower, like below 0.30. e g the single layer low output version of the Atlas - you can most probably still get good sound, but there is a tube challenge. The four tubes in the uber-sensitive first gain stage of the Io need to be ULTRA QUIET. Not just ordinary good quiet. If not, you will get background tube noise. Maybe you don't hear much of it when playing music, but I don't like it anyway. AND if you like to feed the Io with the best tubes, you want the very best NOS in that position. And these can be hard to find, now.
I tested a SUT with the Io and did not like it - sounded good at first but then I noted that it subtracted from the purity, the sound became more hi-fi, for lack of a better word. But that was with a mid level SUT years ago and things could be different now.
I am happy with my Lyra Atlas, I think the synnergy with the Io is good, but it may be that I would have liked the low output version (Atlas SL) even more - with a SUT in between, to help it along. It seems that low output MCs is the main new direction of cart development, now.
