^ without wanting to step on the toes of HDVD800 owners, based on the 1 hour I spent at my local headphone store, to me the amp is nothing to shout about.
At double the price of WA7, I was expected to be swept away by the sound, alas I had put my expectation too high.
I only auditioned with the single-ended cable as Sennheiser Asia was too stingy to loan the dealer the balance cable for HD800 to be used with this amp.
So if you want to run your HD800 single-ended, might as well save your money and get the WA7.
Other users might want to chime in their experienced using the balance cable.
You don't have to worry about tube rolling on WA7 as so far, I only come across 3 brands of 6c45 tubes that can be used on WA7, which are Sovtek, Electro Harmonic and Reflector.