I have over 250 hours of play time on the Icon Mobile now with maybe 50 of those hours on the DAC section. Since I use the IM as a headphone amp only, I only wanted to get some time on the DAC so I would have an idea whether it sounds better than straight out of my iBook. It does.
With my Denon C700s, the midrange had a bit too much energy making it unpleasant for high level sessions. The bass was tighter and more defined with the IM, but it lost some of its oomph over the run in time, maybe because the peakiness in the mids tilted the balance. This prompted me to order a pair of Sennheiser IE8s given their reputation for bass performance and non-elevated mids. I received my IE8s today and after I get some time on them, I'll post a review comparing them to the Denons.
I like the Nuforce. I like the design and so far, it seems to be a well made item. Another member posted links to pictures showing the insides and I thought the board layout looked very clean, especially for the price. By the way, I received an email from Nuforce indicating they would be shipping the replacement plastic piece that solves the issue of some 3.5mm plugs not fitting correctly (I didn't have this problem). I think the sound of the IM is very clean at the upper end with the bass being fairly taut. The dynamics are excellent, both micro and macro. I'm not sure I agree with Headphone Addict's assertion that the Denons are a good match; to my ears at least I would want something to tone down the mids in the Denons as well as let the bass out of the box a bit more.
The customer service at Nuforce is excellent. I come from 25 years in the specialty audio field and have had just about every conceivable experience occur with manufacturers and their reps (a lot of them non-flattering) and would rank Nuforce among the better firms I've dealt with. This is important if ever a problem should arise with one of their products; you want someone there who will take care of your problem.
My earlier recommendation holds.
...these Sennheisers are beginning to sound reaaal good.