It's great, I have the 336C with the DT880 600ohm and absolutely love it! Started with the DT990 600ohm, but they did not sound as natural or balanced (huge bass, very crisp, defined treble, hollow midrange left me wanting for that up close and personal sound).

I am, but I don't have the HD650 cans, but the Beyerdynamic DT880 600ohm. They're a great pairing, now I just have to find time in the day to listen...