So far, I have not had enough time to listen to them any where near as much as I would like. I think both cards benefit from some burn-in, and do sound better, as does the 901 itself, after about 15 minutes of warm-up. Given the amount of time it takes to swap cards (not really difficult, but long enough in terms of quick comparisons) I have been trying to get an impression of what each one can do, one at a time, and will then try to make a true comparison.
That said, both sound much better than the stock card, which is not bad, but cannot compete with its bigger siblings. If I had to make a quick "guess" at this point, I would say that the IEM card has a wider soundstage, and the Minibox a deeper, but narrower one. With speaker setups, you almost always have to chose between the size of the soundstage vs. pinpoint imaging. It's seems like these amp crds show a bit of this. This is a preliminary judgment, so I do reserve the right to change this, but I do think the IEM is the more spacious and airy presentation, the Minibox denser, more palpable and present, but a bit smaller.
I've also been using the Cardas 5813s and the RE600s for this audition, so there's a lot to keep track of. The Cardas and the 600s sound very different, and having the HD/vintage switch comes in handy as well.
More to follow.
Edited by fzman - 8/19/13 at 8:51am