Just a final follow up.
I removed the 2nd CPU, cleared the CMOS but it still POSTs with the 5 beep error. Swapped out all the sticks of RAM, swapped the 1st CPU with the 2nd and swapped out the RAM sticks again. Each combination had the POST error.
I'm throwing in the towel. I thought about buying new RAM since all my RAM is used, but I can't justify spending good money after bad on a hunch it's the RAM. I'm going to part out the Z600 and try to recoup some of my losses.
I just wish there was some other diagnostic method I could apply to figure out what the issue is.
Who knew rebooting, after a year of solid service, would kill the PC.
Thanks everyone.