The Studio Six is only overtly "Tubey" with the right tubes. It is excellent with the HD800's. It also pairs well with the LCD-X and Alpha Prime. I am well into my review and I am impressed at its verstility. I did roll some 6SN7's and a variety of 5U4G variants. Like different frosting on a great cake.
BTW, the Phono Pre amp is fabulous too. The Dynavector is loving that amp.