@me2621a thanks for your really great write up. I have owned a Kenzie for over a year now and feel no need to upgrade. You can get a bit more slam by adding the outboard input transformers. While the 2C52 is a good input tube I love the mid 1960 Telefunken ECC801S (adapter required) in mine. It has a mu of 60 which is fine with my Tung Sol 1626 plenty of gain. The ECC801S has the best midrange and soundstage of any input tube I have tried in the Kenzie. Expensive but worth it, just stay away from any other ECC801S if you decide to try, the later production Siemens are no match for the Diamond Bottom Telefunkens from the '60s. I briefly considered buying an Eddie Current Aficionado so I could run fully balanced from my Yggdrasil to my HD800S but I really love the little Kenzie, it just does so many things well. I would rather put the money into nice powered monitors for those days I would like a change from listening through phones.