First Rate Interface
Great mic-pres. (With or without Unison plug-ins). Versatile routing options—especially for monitoring: alternate speakers, sum-to-mono. A/D and D/A converters are extremely accurate, with stable clocking.
The UAD plugins sound fantastic. I especially love the Unison preamp modeling technology. Admittedly the DUO does not have as much processing as I would like, but that's the tradeoff I made for the price. Of course, the nice thing is that you can daisy-chain UA interfaces and DSP Satellites.
The Console software is also incredible useful. I've worked with a range of large-format consoles, including SSL and API. The Console program from UA takes many of the familiar controls from high-end hardware into the computer: routing, monitoring, cue mixes, and the ability to insert in either the channel or monitor path, to name a few.