MR816 ADAT use

I have three MR’s (2)Csx & (1)x. The MRC816Csx is connected via optical in/out to the MR816x.
My question is while I know I can get direct monitoring of all 16 channels via the 8 outputs of the host MR816Csx will I be able to utilize the other 8 outputs of the ADAT connected MR816x for anything. I’d like to have more than 8 outputs available (with or without direct monitoring) for use with separate Cue mixes etc going to the performers.

I know many of you don’t think you need more than 8 but when you have 7 or 8 performers or even 3 or 4 but each wanting to hear more “snare”, “keys”, two or three various vocal parts, or whatever it’s sure nice to have more at your disposal.

Any input is appreciated. PS - I also have the other MR816Csx daisy chained via firewire and I realize I can not direct monitor anything in or out of that. I use it for ambient or overhead and direct in instruments when I dual mic a guitar amp or some such thing.
Thanks, Ulti