Sorry – this is beyond the capabilities of this forum – given the number of different products involved, it's difficult for us to know what is wrong.
BUT – have you tried the Aggregate Device tutorial in the User Manual ? If not, please do. If you have, did it work ?
If it did work, try the same thing but using the MOTU in place of the H8000.
Note that the recently announced 5.5Beta has new drivers that may (or may not) help.