Thanks guys for the responses. I checked out a few hi-res photos of the Matrix and you're absolutely right, two of the fingers are shorter than the others -- this newb jumped the gun a bit
😮 Since that was not an issue after all, the next step was to remove the bios battery (in addition to hitting CLR CMOS button). Initially everything would boot up into Windows but no display was present on either Intel HDMI or the Matrix. Also, to frustrate things further, the system would intermittently refuse to boot with Code A2, which is IDE detect. How that relates to a GPU beats me. I removed the Matrix and re-enabled multi-gpu rendering in bios. Maybe that was it? That option was enabled before I ran into problems though.
Current status: everything is working properly. Bios confirms x16 in Slot1, Windows and the Nvidia control panel are both happy. I have a feeling this may not last. I will keep everyone updated.
Intel Core i5-2500K : ASUS Maximus V Gene : ASUS Matrix GTX 580 Platinum : ASUS Xonar Essence STX 7.1 :
G.Skill Sniper 16GB : OCZ Vertex 3 240GB : Thermaltake Toughpower Grand 750 : Silverstone TJ08B-E mATX