Hi,
Thanks for responding. Mine is a 6sn7 version (non-SLAM) but SE with preamp out otherwise, and at this moment I don't know where to go for tube alternatives. Anyway, jpr703 is right: the amp is fantastic from the get-go. There's an unmistaken sense of effortless solid power supporting the tubes, and even with my stock tubes I could detect no noise or distortion, not even microphonics. There seems to be an electrical brick wall between the AC line and my headphones.
While waiting for a better pair of cans, I've been listening to the K240DFs and DT831s. The K240DFs opened up tonight, fleshing out Barbara Bonney's voice in several tracks of her lieder CDs. I know it must be a long way until the amp is fully burn-in, and having not heard the X-CAN V3, I bet you won't be disappointed.