Turns out the issue was the on/off switch built into the ATX adapter. http://www.ebay.com/itm/252708495849?_trksid= … K%3AMEBIDX%3AIT
I know I don't need the -5V but I figured it would be easier to test it out of case with the switch. When I powered up the system by shorting the Soft Power pins with a screwdriver it powered up and POST'd.
It recognizes the ram, GPU and calls the K6-2+ "Unknown" but correctly recognizes the clockspeed. However, now I am having an issue where I can't into BIOS because my keyboard inputs aren't registered. I have tried two different PS/2 keyboards, a USB (the motherboard has two USB ports), and a USB in a PS/2 adapter. The PS/2 keyboard small LEDs 'blink' when the system is first powered and when it reaches the POST screen but after that it does not work when prompted to push DEL for Setup.
I made sure I was using the PS/2 for keyboard and not mouse, as well. I also tried swapping the PSU to see if maybe that was the issue but my Seasonic 600W did no better.
-Antec 350W is +3.3V@20A;+5V@20A;+12V1@10A;+12V2@13A;-12V@0.3A; +5VSB@2.5A
-Seasonic 600W is +3.3V@30A, +5V@30A; +12V1@18A, +12V2@18A, -12V@0.8A, +5Vsb@2A
Edit: Vigorous smashing of BOTH Del/Delete keys during POST finally got me into BIOS. However, I am now noticing that any changes made and saved are reset each time I go back. The CMOS battery looks pristine but I imagine it must be no good.