That's a lot of questions...
To answer some of those for you: The "display" only shows volume, no sample rate information. At the moment there is no DSD dac/card available for it. No idea if they are planning to do one. You can easily use it as a DAC or amp only. There are two analog inputs on the back, and there is both a DAC-out and a Pre-out, so you can choose whether to use this unit as an "all in one" headamp, a DAC only or as a preamp for your power amplifier in a speaker system.
Build quality appears to be excellent. I have had mine for a few weeks and it has been playing 24/7. Does not get hot and volume control and buttons/connectors feel good. I was recommended the 1793 DAC option by the (norwegian) distributor as the most "musical and analog sounding" compared to the ESS option. As it is also cheaper, I have not regretted the choice. I can always get the ESS card later if I feel like it, or use an external DAC.
I can't tell you whether it's a good match for LCD-3. I have an LCD-X in the mail that I am hoping will be good with this, but so far I am using it with Beyerdynamic DT770 Pro 80ohm and Fisher Audio FA-002W. My only complaint is that the noise floor is a bit too high for my taste with these sensitive headphones, and I wouldn't expect it to be very different with the LCD-X. I would have loved to have a "pitch black" background to the music. But that's the trade-off for all that power I guess. Don't get me wrong though, other people who have listened to my setup have made no mentions of the noise-floor, only raved about the power and dynamics of the sound.
I'm not sure why you would get this in addition to or to replace the Oppo HA-1 and Moon Neo 430HA in your signature though...? I strongly considered the Oppo but the asking price on it in Norway is currently almost double the US price, so that disqualified it.