The thought on twin gain controls is due to the loss of sensitivity in my left ear by about 4db or so... and why I listen in the nearfield... with the volume moderately up.
Ah, that makes sense now. I'm not aware of any HP amps that have that. I would choose a Balance knob over two volume controls simply for convenience of volume adjustment (supposedly set the balance knob once). The reason those things are not included on headphone amps, of course, is because you are not having to deal with room-generated imbalance since the speakers are right on/in your ears.
The server project sounds like fun too. I use Squeezeserver and have three separate listening areas now. I'm very happy with it except for their crappy, slow interface. I've gotten used to it, but it could be a whole lot better. The actual gear that forms the system is pretty darn good for the money. With tweaks/mods, it is excellent. I have no experience with the other options (Sonos, Olive, etc.) to compare though. I do love having access to a central library of all my music though, and occasionally enjoy internet radio and Pandora as well. Have fun with that!