To daisy chain 2 motu interfaces (or other 8 channel interfaces with lightpipe) you must attach a lightpipe (ADAT) cable to the master interface's INPUT from the second interface's lightpipe OUTPUT. Your master interface IS connected to the computer via firewire. Now DISCONNECT the firewire from the second interface!
This puts your second interface into CONVERTER mode and Logic recognizes its' inputs AFTER you re-set your core audio.
A second lightpipe cable INTO your aux interface FROM your master interface will clock it to the same clock used on the master (word clock, AES, etc..)
Please send me cash for this info.
Took me an hour of futsing to figure it out.