A couple of things:
1. SD claims that multiple non-788t boxes linked together will be sample accurate. Quoting from their "788T Linking with Multiple 7-Series Recorders" Sound Note:
"Linking multiple 702/702T/722/744T Recorders
When two or more of the 702, 702T, 722, or 744T recorders are linked, all linked inputs are sample and phase-accurate. No compensation is required between units."
http://www.sounddevices.com/notes/recorders/linking-multiple-7-series/2. I think the Zaxcom will run 12 channels at 96k. Looking at page 156 of their latest manual, they claim recording at 192k limits you to 6 channels. I guess the assumption is you can record 12 channels at 96k. However, the manual is a bit vague about this point. Like the 788t, the Zaxcom limits the availability of digital effects at higher sample rates. That little DSP must be giving its all at 12 x 96k.
And, for whatever this is worth, it has been my experience that a well designed digital system sounds as good at 48k as it does at 96k. There are many, many other factors much more important than sampling rates. I guess it is nice to be able to point out that one's recorder will go to "11".