I thought the Cute Beyond was a better match with the Grados than the Meier Headfive (which I suppose is like an Arietta), and you could change the opamps to tune the sound if needed. A good PSU will help as well. They are decent low end amps, but I think you would still like a Cavalli CTH, or Millett, or other tube hybrid with the Grados better. I just don't understand the aversion to amps with tubes.
REVIEW: Firestone Audio Amps - Cute Beyond and Fubar III - Head-Fi: Covering Headphones, Earphones and Portable Audio