Ohhhhhkay.

Now the system seems to be registering xl0 interface. Hmmm. I ensured the correct IP was listed in /etc/defaults/rc.conf (don't try this at home, kids! Always use /etc/rc.conf!), moved the riser card and rebooted a couple of times.

Quite odd. I wonder if the whole area isn't prone to electrical funkiness--the power supply is across the machine from the board and that end of the power cable you plug into the computer. There is nothing but a screw between it and the NIC. I ensured earlier it wasn't loose or anything. Very, very strange.

Wish my boss would be cool with actual new hardware instead of new-to-us hardware.