Hi there.
Quite a challenge that I gave up; maybe (hope!) you win.
Ventura here, Asus z10pa-d8 (plain old C612 aka x99 chipset). NO SLEEP, EVEN NO OPTION IN BIOS. Only S4, no S3.
What I've done. Sniffed around a lot, found out that some people do have bios hacks on Chinese x99 dual-cpu boards to have S3 working. Being a little not too brave to take a chance to brick the mobo, I tried to add this via ACPI.
Extracted DSDT and put the _S3 part into it. That's all I've done, no sleep/wake routines patched due to lack of knowledge. The board now DOES go asleep but resets immediately, and the post code says Memory init error (0xbf).
The question is: should I try Runme and post here, or there's guaranteedly no way in hardware (no refresh from 5Vsb etc)? I tried to boot windoze: S4 works as it should...