First:
MOTU hardware is not FireWire, they use FW connector and hardware but they run their own propietary protocol so MOTU hardware is not meant to be used used with Firewire devices.
edit:
Oops, I was only thinking of MOTU's PCI Audio devices, the text above refers to them. MOTU has standard FW audio interfaces too.
But in general, you can daisy-chain firewire devices, therefore the 2 ports exists
like this: computer - Audiointerface - External HD
The connections you mentioned were exactly the wrong ones
(although you can connect computer to computer with firewire, and have a hub in between them atlhough I suspect that using a audiointterface as a hub between computer is nothing but trouble)
Do NOT make double wiring setups!
-Tomi