Two things I do know. SCSI chains are extremely sensitive to termination issues: if they are not properly terminated the resulting noise on the SCSI bus can lead to all manner of grief. The basic rules of SCSI are 1: keep it short, 2: keep it neat, and 3: you must have a proper termination at the end of the daisychain. Sounds like you have that now, so this is just a rehash for anyone who doesn't know that.
The other thing comes from having done some extensive altavista and dejanews searches when trying to choose a backup device to buy for my D1624. You don't want to hear this, probably- but please don't shoot the messenger. The consensus on dejanews was that the Orb drive/Fostex _anything_ combination was extremely flakey (even when it did appear to work), and worse yet that it would appear to work for backups, but then _fail for restores_- leading to a false sense of security and irretrieveably lost data. I saw roughly 15 articles claiming that the Orb drive was little more than a doorstop when used with a Fostex box, and only one from someone who was having success with it. And that same person later posted an article describing a restore failure, IIRC.
I don't know this for sure, but it appeared to me based on those articles that the Orb drive was not a win. But don't feel bad: instead of an Orb, I foolishly bought a Yamaha CD-RW drive to backup onto, and the Fostex can't write to it at all. It just sits and grinds forever. Looks like their list of "operation-confirmed" drives from the website is for real. Don't just take my word for it, though- do the dejanews search on Fostex and orb...
I'm a little burned, too. Sorry for the bad news, but it may not be possible to get the Orb drive to work reliably. Sigh.