[Darryl Ramm]

Guaranteed by who? Avid or any vendor is unlikely to give you a guarantee that any third party box works with their stuff.

Presumably you mean as an ADAT preamp? The 880 can also operate as an analog preamp.

Incompatibility between ADAT products is virtually unheard of, the main technical issue is wether both sides support the suitable SMUX spec if wanting to run at high sample rates.

The MBox Studio should work with all ADAT preamps, given the limitation it only has one ADAT input...and if you want to run above 48 kHz hopefully it supports SMUX for faster sample rates/reduced channel counts, but Avid does not seem to mention that in the product specs).

Most problems will be user error, improper ADAT cable connections, improper sample rate settings, improper clocking, improper optical format. If you are having problems set stuff up the most simple way to start, everything running at 44.1 kHz or 48kHz, the ADAT preamp set to clock internally and set as the clock source for the Mbox/Pro Tools, the preamp main/first ADAT output connected to the ADAT input on the interface. Make sure the MBox Toslink optical input is set to ADAT not S/PDIF.