Did reinstall of Audio drivers and updated the Asus X79 BISO. Reseated all the audio cables and HD97 motherboard connection.
It is listed but just says Not plugged in with a red arrow. Its like whatever way it detects that you have an audio cable (speakers) plugged in is broken. I know its still working though. I can change the front panel mic and headset ports to AC97 from HD and I can then get sound out of only that headphone port but it wont even try the back panel and I dont see a way to force it to. Like it just thinks that nothing is plugged in so it disables it. I tried putting the 7970 back in and did a system restore but no luck. I even have a Windows 8 test OS that I had used in the past and it cant see the speakers plugged in either. So I think something got fried. Not sure how though, Im always really carful and everything was turned off.
Did you try doing a total reflash of your BIOS with the reset flags for the DMI reset? I don't know if this applies. But I always reformat when I install a new video card. It usually solves some OS/Game issues that I have when I get new hardware.
Also, aside from the lack of audio. How does the 290X handle with your 30 inch monitor? Was it noticeable upgrade going from the HD 7970 to a 290X at 2560x1600 gaming?
If the onboard audio died on you. You can always get a Creative Titanium HD (or the Z series) and enjoy high quality audio