Well for ScienceOne's use .... he has the Octopre which is an 8 channel preamp that has the A/D D/A built into it. It's signals are transfered via ADAT.
There are many 8 channel preamps out now that offer ADAT connectivity, though in his case the 1010 doesn't offer ADAT I/O so he needs an interface such as the ones listed to utilize the ADAT I/O of the Octopre.
In essence, using the ADAT interface and the 8 channel ADAT preamp, he is basically adding a second 8 channel soundcard to his setup.
Hope this clears things up for you.
-Edit to add- monitoring can be had from either the 1010 or one of the 8 channel ADAT preamps. Provided, of course, that the preamp offers ADAT IN and analog out.