Well, I may have found the answer myself, which would be : no.
The SATA power connector on the DQ77KB is stated to provide (technical spec, page 76) up to 26.15W, but my 4 hard drives would require up to 37W on startup (no staggering spin up on this motherboard).
So i don't think it would work. Maybe with only 3 hard drives, but i need the four of them.
Hoping this wold be of help to others - I'm planning to use 3 Intel SSD hdd's rated at 5v, 1 amp for a 15 watts total power for the HDD's and a Slot Load DVD using 5v, 1.3 amp for a total 21.5 watts of power. I think or the using the internal Sata power header and requiring four HDD's you might try using four Sata SSD's at 5v, 1 amp and an external Optical Drive with it's own power.
Another option might be like my configuration and include a mSata SSD for booting.
Thank you for your answer, unfortunately this solution is not for me as the configuration i was planning was for a NAS server, and i already have the 4 hdds. Using SSDs instead would bring not enough storage, even though it would be speedy.
I liked a lot the idea of having a mSATA SSD for the OS, but i found a mini ITX motherboard with the same chipset (Q77), but with standard ATX power connector, and 6 SATA connectors, so i can use a more traditionnal 2.5" SSD with this solution, and also my 4 HDDs.
I dont't need thin ITX form factor, so the DQ77KB is not the one for me...