To the other Al.. Appreciate the thumbnail impression of the HDVD800 chractersistics and performance. Have you tested it with HD800 and HD650 cans?
I have both the HD 800 and the HDVD 800, though I am still awaiting the construction of a balanced cable to replace the stock Sennheiser single-ended cable that comes with the HD 800.
I have VERY little to compare to, so it is hard / impossible for me to compare this combination to other amps for the HD 800.
That said, the sound of the pair is excellent. One hears concerns that the HD 800 can have sibilant or shouty trebles, particularly on less-than-great recordings. I have not observed that at all.
Others worry that the HD 800 is rather weak in the bass, at least compared to something like the Audeze LCD2, 2.2, 3, X, ... I have found the HD-HDVD 800 pairing to be ACCURATE in bass representation, presenting a natural source such as an orchestra with the same amount of bass you would expect in a live concert. It is of course hard to comment on amplified sources, as their bass level seems to depend upon the tastes of the engineer with that particular knob in his hand.
I have tried the HDVD 800 on the HD 650 as well. More importantly, the owner of the HD 650 has tried it (better, because he can compare it to whatever he is accustomed to driving his HD 650 with). Again, the results are superb. He reports great satisfaction with it.
I have also tried the HDVD 800 on various Grado headphones. Since their input impedance is so much lower (32 ohms) than the nominal input impedance of the HD 800 for which the HDVD 800 was designed (300 ohms), this could be an issue.
It is not. Sounds good to me. But more importantly, the HDVD 800, despite its 43 ohm (or thereabouts) output impedance, as heard by a person more experienced in listening than me (for example, he found flaws in my beloved Grados!!), sounded very good and better than the Sony PHA-1, which is a portable DAC/amp that directly decodes the iPod connector digital stream (no small feat... it is not the same as USB!).
Sound will only get better when my balanced cable becomes part of the signal chain, but I can state so far not only complete satisfaction but pure delight in the combination. The ONLY time I have heard it fall the tiniest bit short of something else is when I played the rock version of
Carmina Burana by Ray Manzarek. Grados, known for their excellence with rock guitar, actually give a better sound for this piece (in my opinion, of course) - more transparent, more "you are there." This excellence of the Grados on this piece persists whether you run them through the HDVD 800, the Sony PHA-1, or direct from the iPod headphone output.