I thought I should mention this in case someone has a similar problem. It never really occurred to me to try different combinations of hard drives connected to the Firewire port together with the FF400. However, by accident I was running everything with just a 1TB WD MyBook formatted in FAT32 going to the MBP and the Fireface connected to the HD with a FW800->400 cable. Suddenly, the system became stable.

So, I don't know if the issue is the chipsets on some of the other manufacturers' drives, or the fact that they're in HFS in my case (I did try disabling Apple's HFS driver, which didn't make a difference, so it would seem it's about the chipsets -- but who knows).

In any case, if you're getting BSODs with a similar system, experiment with the hard drives if you can. I suppose instead of a hard drive you might also get a Firewire hub that has a compatible chipset. Unfortunately it seems to be quite hard to find out what chipsets are on hard drives or hubs. Maybe we should have a database where people can submit compatible hard drives and hubs?