I have this and the dedicated DAC/Monitor Controller from Crane Song, the Avocet. The HEDD and Avocet (most recent models) have the same DAC. These converters are used by some of the leading Mastering engineers in the world for their neutrality. At this level, choosing another DAC would simply be a matter of preference; speaking from an audio engineer's perspective these converters are as accurate as it gets (we don't use words like "better" for high-end conversion).
Now, why would audiophiles be interested in this ADC/DAC? Well, if you like the sound of Tubes and Analog Tape, keep reading...
Dave Hill, the mastermind behind this box created a proprietary set of DSP processes in this box that emulates the sound of tubes (Pentode/Triode) and analog tape. In Audio Mastering, these processes are used to give digital recordings that might sound a little lifeless more coloration. The Tape process emulates the sound of an analog mastering deck in a way that sounds like the real thing, and not found on any digital effects plug-in, and the same goes for the tube processes. It is capable of adding harmonic distortion that isn't in the original recordings, and it can go from subtle (like the harmonic distortion you would hear on a Pink Floyd record) to "crunchy" (like the distortion you would hear on early Motown stuff).
I would imagine that any audiophile with a serious Solid State playback system could make their rig sound like they've got several high end Tube amps (because you can adjust the Pentode and Triode processes to your heart's desire) and a 1/2" analog mastering deck (without tape hiss, the process is intended to emulate the dynamic range compression effect of recording to a high-end analog deck). A lot of the albums that are mastered (I'm talking about the high-fidelity ones here, not the super distorted crap that pollutes most of our airwaves) have been done using this ADC and it's been proven to give that elusive "analog tape and tube" sound that was heard on recordings from the good ol' days, that said, the effects can also be very subtle or completely bypassable if you just want to accurate conversion. This ADC/DAC is very well known to the best engineers in the audio industry, how that would apply to an audiophile's living room or den is left to the imagination and taste of the user.
I currently don't have enough time to do this for my own personal enjoyment, but I've been transferring some of my older CDs (early generation CDs that sounded "cold" because the converters at the time weren't top notch) and have been processing them through the HEDD to give them more coloration at varying degrees depending on the album. Not only is the result "warmer" than the original CD, but the quality of the HEDD's harmonic distortion is often able to give the transfers more depth that I haven't been able to achieve using other digital processing effects.
I know for sure I won't be upgrading my ADC in the foreseeable future! I just wish I had more spare time to use this box for my own personal enjoyment (currently, 90% of its use is for Audio Mastering projects and it's one of the tools in my arsenal that I consider essential).