MR Setting For Mixing And For Recording


I am using MR816CSX for recording and for mixing using its onboard effects.

In its settings, I have Digital I/O, Effect set to ‘External Effect’ how ever I am not sure when to use each of the four options:

8 mono
4 stereo
3xstereo + Rev-X

Which setting should I use when I am recording with MR as analog I/O?
Which setting should I use when I am using MR as external effect ( not recording). Say I have 2 mono and 2 stereo channels.

My other question is that how come I get from time to time “Rev-x Not available” and “Channel Strip” not available when I try to insert them in the audio channels.

I do greatly appreciate this if you clarify this. I have spend so much time reading manual and asking on forum. No one can help.

Thank you.