Okay, at the risk of jinxing myself here, I think the new firmware fixed my system lockup problem.
I re-installed my card without any disks attached. I then downloaded the firmware that was linked here previously (
http://www.sonnettech.com/support/downloads/software/temposata_212.zip) and it updated my card, with my system booted in Leopard. I almost thought the firmware was hosed while updating, as it stopped about 1/8 inch along the way into the progress bar. After 3 minutes or so of waiting patiently, it filled in the rest of the progress bar almost instantly and said it completed successfully. I then rebooted as instructed upon exiting the installer.
I booted up my machine again without the disks installed, just to double check it would still boot (and not freeze) after the firmware upgrade. I let it run 5 minutes or so, then shutdown the system and plugged in my 4 external SATA cables to my external disk chassis, and powered everything up. It has now been 15 minutes + and my system does not lock up any longer. I have Four 300GB Western Digital disks in a RAID setup, and all my data is back (Whew!).
Hope this helps the rest of the group!