Quadro K5000 CUDA support not working on Mac Pro 2008

I’m running a Mac Pro 2008 on OS X 10.11.6 El Capitan.

I just bought a Quadro K5000 on eBay for CUDA support while using After Effects CC 2017.

The new card is installed but CUDA support is still greyed out in After Effects. Updated drivers but no luck.

This is the only reason I bought the card. Can you please help?