Well I received my DAH1 Mark last Wednesday and have been enjoying it ever since. I use this DAC primarily in a loudspeaker setup, although I have used the headphone amp section a few times.
I use the DACOUT outputs into my NAD T162 preamp via Kimber PBJ interconnects, which is then fed out to two NAD C272 amps running in bridged mode via Kimber Timbre interconnects. The amps then run out to a pair of Dali Ikon 6 towers via Kimber 4TC/8TC shotgunned biwire speaker cables. The source of the digital stream is an iBook G4 via USB, using the Cog media player for flac files only.
Through this configuration, the DAH1 sounds very enjoyable. Tonality across the spectrum is mostly neutral, but with a slight tendency towards the bright side (this may gradually recess with more burn-in). I have not experienced any signs of listening fatigue, and has that "I could listen to this all day long" feel. Soundstage width is great, although the depth seems a bit poor; there is a flat feeling when it comes to soundstage depth. Inner harmonies sound thick and rather rich, but not muddy. Overall I find this DAC to have a very "analog" sound. Dynamics are fantastic, and the unit provides plenty of "snap" with these amps. Even microdynamics are executed nicely. A very good sense of rhythm is created by the DAH1, which adds to the toe-tapping factor.
One thing to note about this unit is that if you are planning on using this in a loudspeaker setup as a preamp, you may want to reconsider. When I use the LINE OUT jacks directly into my NAD C272 amps (bypassing the T162 preamp), there is a VERY annoying hum/buzz sound that is so loud, it makes it unlistenable in this configuration. I plan on sending an email to the seller about this, because I do notice a greater level of transparency when using this configuration, but the buzzing sound practically gives me a headache.
As for the headphone amp section, it is quite a few notches above my iBasso D2 Boa. When listening to my Beyerdynamic DT770 Pro 80s, the bass is much tighter, things are more dynamic, and more alive in general. It also has a smoother, more natural sound than the D2, but doesn't sacrifice any detail; in fact, it provides much greater detail than the D2.
Conclusion: For $325, with all the features this unit provides, I think it is a great deal. It's unfortunate that it makes that terrible buzzing sound when using it as a preamp, but I'm fortunate to have another preamp I can use instead. The headphone amp section is very good, which I'm sure is the main concern for most people on this site. All in all, a good buy.
Strengths: Smooth, neutral tone, good tight bass, great soundstage width, good dynamics/microdynamics, timing, no listening fatigue.
Weaknesses: Poor soundstage depth, a tad bright (but not annoyingly), buzzing noise when used as a preamp.
***EDIT*** Keep in mind I only have about 25 hours tops on this unit. I'm holding out hope that the soundstage depth will improve with more burn-in. I will report back.