Wow, just checked back to this thread after a few weeks and there is a load of excess testosterone flying around.
So, I am a sound engineer, I have been working professionally for long enough to know I can trust my ears. In My studio I have a variety of interfaces, Protools 192s, motu 828s, Mbox2 pro, Apogee PSX-100, and yes a Duet too.
Firstly LogicPro, I hope your friend wont mind you screwing his Mbox as, if it is the same model as mine, it is a complete bitch to get inside; good luck with the photos there.
Secondly, what good are photos in deciding how something sounds? Surely that is what is important here. Do I care if they all have the same chips in if the rest of the design has such an influence on the final sound recorded and reproduced? Don't bother doing the photos as they wont prove anything, use your ears instead....
As has been mentioned before, there is an awful lot more to making a great sounding AD than merely the converters, all the other components play a large part in what you finally hear, especially the clock. The first thing I do upon receiving a new bit of gear is to AB it with something comparable I already own. In this case it was the newly purchased Duet vs Mbox2pro and PTHD-192s. It was a close call between the 192 and the Duet, and imo the 192s won (not surprising really considering). Next up was the Mbox, which I have to say fell rather short. Recording an identical signal into both boxes simultaneously then comparing them out of the same converter, the duet was much more transparent and defined than the Mbox, especially on acoustic sources. As for playback, again the Duet sounded better (imo), similarly transparent etc...
The duet certainly doesn't equal Hi end/professional gear, but considering the price, portability and sound when compared to its similarly priced peers I reckon it is the best of the bunch.
When I have a moment, which wont be until after the weekend (maybe even wednesday as it is my stag night on Saturday....) I will do the same test again. Obviously you can only judge the recorded signals through whatever system you have and won't ever be able to do the playback test without having all the gear in front of you so you'll have to trust me as far as playback goes....
I doubt it will do anything to slow the testosterone tsunami but thought I'd let you know my opinion.
What source are you recording?
I've only got a HD192 rig right now, but I'm interested in hearing the difference in terms of input quality of the three.
If possible, could you please upload the three files in WAV format?