pound for pound, dollar for dollar, perhaps best 2-ch FW interface available
While there are perhaps better sounding two channel A/D/A converters available (though not many), I doubt there are any that can touch the ULN2 in terms of features and price.
The 2D card was an amazing upgrade to this box, and for the moment at least, it truly is, as the mfg. Metric Halo says, "future proof". Capable of fully professional results in any scenario, the little ULN2 punches far above its weight it terms of clean, accurate sound, and excellent quality A/D/A conversion.
I have owned and used these boxes literally since they were first introduced, and I have never regretted my choice. I would not say the pre-amps sound like a Millennia, which I also use - the ULN2 has way more gain!
Well, it also sounds a touch "drier" and less "3-D" than the Millennia, but still a very usable pair of pres.
And you can connect other pre's via ADAT optical, SPDIF, or AES, digitally, so although the ULN2 started life as a simple 2-ch. interface, since the development of the 2D card, its capabilities have increased significantly.
MH is legendary for their customer support, and although the box is built like the proverbial tank, the software is very sophisticated and certainly user questions will arise, but are generally handled quickly and courteously, IME.
The ULN2-2D is an excellent value, performs at a very high professional level, and would be a fine addition to anyone's Mac-based rig.