Would like to confirm, that simply changing my HD 6870 to a used GTX 760 (and downloading the Nvidia web drivers), solved the waking from sleep issue for me.
I have set SMBIOS to iMac 14,2 as it gives better FPS in cinebench than Mac Pro 3,1. However, other than that, the Mac goes to sleep fine and wakes up fine.
I sold my 6870 for £45 and bought a GTX 760 for £65, so all in all not too bad.
I tried a 750 TI, sleep worked, but I could only get a fixed resolution of 1344 X 756, I have an apple display capable of 2560 x 1440 as well as multiple resolutions. I downloaded and tested with the new drivers and went through the setup procedure, but no luck. Are you able to get multiple resolutions for your monitor or is it fixed like I had?
I gave up and went back to Yosemite for now, I still have El Capitan on a second drive so I can switch back easily.
I think the Apple Developers are laughing.
Yup, I'm on 10.11.3 using the Nvidia Drivers and am running two 23" Full HD monitors at 1920x1080.
I'm using the 2 DVI ports if that helps.
Updated 10.11.3 El Capitan and radeon awake without problems.
My configuration:
1. bios main onboard, and always active.
2. Secondary Radeon.
The start will be blind,, but I've had success with this configuration. As for the acceleration I unplugged the onboard, and perfect.
I restarted only plugged Radeon and wake up smoothly and acceleration ok. Only I had plugged during migration to El Capitan Yosemite the Onboard.
USB, sound, everything ok.
Cheers
Could you elaborate a little more on your configuration?
Are you bridging radeons?
Is there a way for the wake to work with only one radeon..?