The routing for that is inconsequential really. The question you need to ask yourself is can my computer through Pro Tools function with the firewire drive? Typically, external drives cannot be used for recording audio in real time. They are mostly used for transferring data and playback. What errors have you been receiving and what are you doing when they occur? Pro Tools will usually give you an error code stating "DAE error -XXXX". You can find the reasoning behind these through a quick search in google, but your system is quite old. I've got the Digi 003 at the moment, so I'm sure you know of the obsolescence.
Let me know if I can clear anything else up.
-Trapper