I am surprised that this AMP is pretty lightweight. It works super well with the HD800.
I just gave 2 because the one I received had 5-6 easily noticeable scratches on the top and front panel which was disappointed.
They say that Sennheiser HD650 and up like tube amps. I tried a few mid grade tube amps and wasn't impressed. I liked my HD650 with a Schiit Magni 3 better than any $300-$500 tube amp, and I went through LOTS of tubes to get THE sound. No luck.
Got a great deal on a used HD800S and didn't want to mess around and go halfway, so I got an amp designed for this headphone, the HDVD800. Absolutely awesome. NO REGRETS! If you're looking for an amp for harder to drive headphones, look no further.