No sound through displayport on MacPro 2010?

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Hi everyone. I recently installed at GTX 970 card in my mid 2010 MacPro and hooked it up to a Samsung u32d970q monitor via displayport. I thought it'd be nice to use the display's onboard speakers but when I go to the sound panel in System Preferences, there's no option for displayport sound output. (I only have headphones, line out, and digital out). The sound on the monitor and on my computer is turned up enough. Is this a limitation of running (unflashed) nvidia cards on older machines or am I missing something? I'm running the most up to date nvidia web drivers and El Capitan, 10.11.1. If anyone has any thoughts, it'd be very appreciated.

 

[h9826790]

https://forums.macrumors.com/threads/guide-hdmi-audio.1499797/

 

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Thanks so much. Reading through all the posts now to figure out how it'll work with El Capitan but this thread should be the solution.