IMHO, HD800 should be driven by a tube amplifier.
I'm using an OTL Amplifier with two 5998 tube and the HD800 performs superbly.
I've owned a Stax system with L700 headphone and 006Ts amplifer (with tubes RCA Clear Top) for one year together with the HD800.
At the end, comparing the two systems, i decided to sell the Stax system.
The HD800 in my setup was significantly outperforming the Stax.
Just my two cents.
Carlo
I'm using an OTL Amplifier with two 5998 tube and the HD800 performs superbly.
I've owned a Stax system with L700 headphone and 006Ts amplifer (with tubes RCA Clear Top) for one year together with the HD800.
At the end, comparing the two systems, i decided to sell the Stax system.
The HD800 in my setup was significantly outperforming the Stax.
Just my two cents.
Carlo