I believe at this point the lack of bass emphasis with the Grace is a combination of the HD-650 roll off, impedance as a function of frequency on the low end, and the brightness of the amp. The hardest thing for amps to do, in general, is to produce solid well controlled bass. Same goes for headphones really.
The Grace is fatiguing compared to the Ultra Desktop. If you are going for pure sound enjoyment then the Ultra is more pleasant, the Grace is a bit too analytical.
Thanks for taking the time... Pity you'd say that. The Grace possessed many features I found desirable.