I have been using the Conductor for approximately a month now, initially with HD800s but then with ATH-W3000ANVs from last Friday, some of my impressions:
Current setup is:
iPod classic > Wadia 171i transport > Burson Conductor > W3000ANV
With the HD800s I was experimenting with the different gain settings and it appeared that, at the same volume (though I had no way of measuring), the low gain seemed slightly more relaxed and laid-back than medium or high gain. But the difference was small so I'm not sure if it's an actual difference or just my hearing. I settled on medium gain for the HD800s.
The pairing is very good in terms of detail, soundstage and linearity, no specific part of the frequency range dominates, and I felt it produced a particularly realistic sound with acoustic/live music, and is perfectly capable with other genres.
However, I felt I needed something that could complement the HD800s, hence the W3000s, and I have to say the Conductor/W3000 pairing is phenomenal to my ears.
The Conductor is at low gain for the W3000s, either 9 o'clock or one step higher on the volume. The sound is rich and deep, more than enough bass, certainly when coming from the HD800s, but still with exceptional detail retrieval.
I feel like nothing is given up when switching away from the HD800, but the W3000 gives me a far greater sense of euphony and musicality, which is tremendously addictive; there is no urge to "notice" any small things in the songs but instead just to get lost in the music.