FireWire 400 Devices Incompatible with FireWire 800 Macs?

If anyone knows of a solution to this, it'd sure come in handy.... I'm dealing with several converters that turn analog audio/video signals into standard DV video. All of them use the FireWire 400 interface, as is traditional for DV devices. My problem is that my Mac, a Mac Pro (4,1), has FireWire 800 ports. I've bought two different FireWire 400-to-800 adapters, both of which make the DV encoder