|"When I press Enter on the NIC to enable it as a boot device, it's supposed to open up the options with a sub menu for the NIC"|
I've never seen it presented that way in any BIOS Setup I've been in (and that's quite a few). Usually, in BIOS Setup, you need to select BOOT in the top menu. You then get three, four or five boxes to set each boot device in your preferred order.
Then it's F10 to save and exit.