The tuberolling on my Air Tight was something incredible... why? I never tought that just one only tube (I'm referring to the rectifier one), can tune the sound, trust me !!! I have tested a very BIG quantity of tubes, as power the new production WE are the best (I have also AVVT c-37). Mullard 12au7a NOS cryo 1955 long plate are the very best. RCA 12bh7a are the very best, and Tung Sol 5u4gb is the very best.
These tubes are selected with Shunyata Anacondas power cords... If I change the power cords, I need to put others tubes, especiallly the rectifier one. And more... these tubes are the best with the Air Tight dumping factor to the 2 position and after the internal regulation of the hum trimmers.
These tubes are selected with THIS K1000, (I had 7 K1000 at the same time) and this SN 11316 is the best of all the others).
I tried the TOP Acrolink power cord, but the Anaconda are the very best for the K1000. The best IC is the Acrolink (TOP), I tried the Shunyata Antares, but the Acrolink goes much better.
About the BAT integrated, as I told, is very good, but in my experience the K1000 needs a bit of negative feedback and you can regulate this on the Air Tight, (dumping factor), this is the reason I think that even the Zanden (but I never heard it), can't match the Air Tight ATM-300 (for the K1000).
I can't remember another sound like this... no any other headphones , no speakers... it's a different way to listen and enter IN the music !