I have tried the HeadBox and although it's well priced for it's funcunality (two headphones jacks, multiple inputs etc.) and it can actually act as a pre-amp, it was sonically inferrior.
It lacked the dynamic, sound compressed and...
As a proud owner of the Aqua amp I can say that the match to the HD-600 is phenomenal.
I've compered the Aqua Head to the Creek and Musical-Fidalety and the Head-Box from Project and I liked the Aqua better.
Much more quieter and much...