The two hard drives I have are Buffalo drives with 4pin, 6pin, usb 2 connections. I am using the 6 pin for best results. Using a firewire 400 Belkin hub that now connects to my new imac i3. I had this hub already. I will in the future want a 800 hub. A connection from a firewire 4 pin on the hard drive to the hub 6 pin connector does work, as well as a 6 pin hub (400) to the 9 pin (800), where I hooked up from the hub to the imac. Found that these are backwards compatible. All I had to get was a 800 to 400 cable. As I stated I opted for the 6pin on the hard drive to the 6pin to 400 hub connection. Then had a 6pin on one end of the cable to the 9pin for the imac.
Having only one firewire 800 on the imac doesn't help. you can also hook up straight from the hard drive to the usb connection on the imac. You can also get a usb hub 2.0 hub if needed.
Here is the best links and info I found on the subject. Jon L