I have a Trafomatic Head One and a Goldpoint Headphone Pro V9 and Auditor currently...
Scrap the Auditor it´s optimized for high impedance headphones. While the ED 8 is not bad on it by any means. It´s so efficient the amp really has to be bad for it to be bad... If rumble is your main criteria yout will get that but I rather trade it for fast punches. Rumble leads to some congestion and it´s not the ED 8s nature to congest. Not even unamped it congests...
Anyway it´s not on the level of either my Goldpoint headphone Pro or Trafomatic head one for any of my low impedance headphones. The ed 8 is truly spectacular on those two amps so it can do great
on both tubes and solid state obviously. I need more time to give a final verdict but if you only need an amp and no preamp or dual input functions. Have no high impedance headphones and budget oriented the GHP is a no brainer really. If you are space limited it´s more then 6x smaller and 6x lighter so it has a lot going for it.
Head one is surely fancy looking and will make you positively biased just on looks though ;)
But anyway the head one and Headphone Pro have VERY similar signatures. The Head one is certainly a very serious tube amp not much colouration in it that´s for sure. Both these make music sound more natural then ever to my ears.