I have the A18-D18 combo powering my HD800.
Still RCA connected and stock single ended Sennheiser cable.
Don't have a lot to compare with,but like Project86 allready tolled us at his reviews,a VERY good match with the HD800.
Absolutely loving the sound,endgame for me.
Yulong used the HD800 to tune his amp if I am correct.
I have to crank it up rather far though ,around 4 o'clock.I like to listen loud...
Don't know if balanced wiring will change that,haven't...