I'm pretty sure you can use the es8 as a standalone ADAT expander - don't use the usb and connect the ADAT I/O to the ADAT I?O of your Motu... the extra channels will show up as part of the Motu in your DAW
check the manual - it's easily accessible on the ES site!
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities