Hi all - I feel pretty dumb about this, but I am having trouble figuring out which FW cable I need to use on my late 2009 iMac. I bought Amazon's IEEE 1394 4-Pin/6-Pin FW Cable but it doesn't fit into my iMac's port. The 6-Pin jack fits into my external HD fine. The only other FW cables I've ever had are 6-Pin to 6-Pin. I've only been using USB since I got the iMac, but found an old drive I want to attach. What the heck do I need to get to fit into my iMac? Thanks in advance!