I hope people don't mind if I return this thread back to the original topic, but I would like to add my comments about the Apogee Duet.
I had been debating getting the Duet for some time, but after reading the beginning of this thread and my purchase of a MacBook Pro led me to pull the trigger on a used one. I have been very happy I did. I will break out my experiences by the different uses I have for it:
As an A/D converter, I am very happy with it. As a test I copied a good sounding CD and then compared the copy and the original. Both through the duet and through my Birdland Audio Odeon-Ag using a Sugden Headmaster for a headphone amp, I was hard pressed to tell any difference. Doing the same test with my M-Audio Firewire that I had been using, I detected a slight congestion with the copy. I also copied a recent LP with excellent results. One of my projects is to digitize some reel-to-reel tapes that I have so I can get rid of them, as well as archive some LPs, and I feel the duet will do the job extremely well. It is also very easy and convenient to use. I like the large volume knob and the LED indicators.
As a D/A converter, I compared it to the Birdland DAC (
Birdland Audio - Odeon DAC / pre-amplifier) which costs over twice as much and doesn't do A/D. I preferred the Birdland, but not by a wide margin. The duet was slightly softer and less focused but still extremely musical. The Birdland is fairly compact but requires AC and either optical or coaxial inputs. I use it with the optical output of my iMac and with a OPPO player. Of course comparing the duet to the built in DAC in the MacBook or iMac, the duet was substantially better.
As a Headphone amp, I had read that the duet was quite good but was surprised at just how good it was. I thought I could always have the duet feed my Mini3 (a version without output resistors which sounds very close to the Hornet M that I used to have) if I wanted a little better sound, but I actually much prefer the duet's output, at least with low impedance headphones. The duet sounded much more spacious, and had a surprising amount of bass slam (something that the Mini3 is pretty good at) that I thought might be missing. It wasn't quite as good as the Sugden Headmaster which was also very spacious (maybe a bit more so) and the Sugden had a little better detail. But again the Sugden is not portable and costs much more. I tried the duet with AT A900 and L3000, Grado SR80, and Yuin PK1 all with great success. I also tried it with the higher impedance Senn. HD580, AKG 240 and the 600 ohm Beyer DT 990, and in each case the output level was too limited, which isn't too surprising since the duet is powered from the Firewire port so will have limited voltage swings.
Bottom line: I agree, the Apogee Duet ROCKS!