I find the HA-1 to be excellent with every headphone have except the HD800, which is the only intrinsically bright headphone of the bunch. But the HA-1 DAC+amp is a little bright, in my opinion - perfect for my LCD-2 rev.1 and OPPO PM-1.
For the HD800, I started out bypassing the HA-1's ESS9018 DAC with a Metrum Acoustics Octave MkII (NOS DAC) while still using the amp section and that did wonders, but it was still a little bit brittle - sounding really great for the first 10 minutes or so, but then the fatigue would start to set in (with the HD800).
Replacing the HA-1 amp section with a NuForce HA-200 (single-ended, Class A amp) was a "final solution" for the HD800 (using the Octave MkII DAC) and I could still be happy with that, I'm sure, but I jumped at a good deal on the Metrum Aurix amp and it has proven to be just a wee bit smoother yet more detailed than the HA-200. The Aurix hasn't offered as much bang for the buck at improving the HD800 as compared to getting the Octave MkII, as it's really only slightly nicer than the very affordable NuForce HA-200.
So... I no longer use any part of the HA-1 with the HD800, but love using its amp section with everything else.
There, I broke the ice for you.
How did you "fix" your HA-1 to pacify the finicky HD800?
Mike