I would certainly rate the HD24XR (A-D and D-A) converters alongside the Ensemble and similar quality units. They are not in the very top league of stereo mastering converters, but on a per-channel basis are very good.Hey Boswell, thank you again. I read the manual regarding this and I understand the limitations. They are fine for my planned usage of the unit at this stage. I would be sending 16 x 96KHz audio stems / instruments from logic via the 16 firewire channels to the unit to complete the final mix in the analog domain. Capturing the final mix file on a device like the HD24XR is a very good piece of advice for a transparent final file. A second bounce to that machine could also produce a 44.1KHz version avoiding any SRC inside a DAW at any time. My main query about this unit is whether the D/A converters sound as good as other high end audio interfaces like the Apogee Ensemble or Apollo. What's worth noting, especially for those producing their own masters, is that you can supply 96KHz masters to I-tunes for distribution, as they have optimised their conversion software to create the AAC and MP3 files from this resolution. There is a very good article about that here http://images.apple.com/itunes/mastered-for-itunes/docs/mastered_for_itunes.pdf including info on how to use their software to test how your tracks will sound after the conversions.
I know your plan is to source from the D-A converters in a Zed-R16 at 96KHz, but if you wanted to use HD24XRs instead, you would need two HD24XR units, as each has the capability of 24 channels at standard rates or 12 channels at higher rates.
If using an HD24XR to re-capture a 44.1KHz stereo mix, it's advisable to clock the HD24 from an external source, as its internal 44.1KHz clock is stable but slightly inaccurate. This HD24XR can't, of course, be the same HD24XR as you are using as a 96KHz source device.