maybe a PCIe card would be better?
the sonnet tango adds 3 FW800 and 2 USB (never enough of those) for 110$
http://eshop.macsales.com/item/Sonnet%20Technology/FW8USB2AE/
the aaxeon adds 2 FW800 and one 400 for 68$
http://eshop.macsales.com/item/Aaxeon/FWB68300/
..
do you have FW400 drives in your mix? Do you daisy chain them into the FW800 drives? A 400 drive in an 800 chain will bring all the drives down to 400.
note that plugging FW drives into their own outlet on a hub is the same as daisy chaining as far as bandwidth sharing. 10 drives in a hub working at the same time will give you 1/10th the bandwidth, the same as if they were daisy chained.
in a card, bandwidth is independant.