I have a similar question, though am not lacking in documentation like the original poster above me. Is it okay to install both Assistant Fans to suck air from the bottom-right and blow it out top-left (Rear of case)?

I know the manual only says to place the Assistant Fans so that the fans propel air towards the lower front of the case, but that's just sucking hot air through the motherboard... (Computer case is designed to dump hot air out the back of the case, below the intake vents for the Assistant Fans).

To the original poster, you should at the very least have both fans facing the same way as each other. You don't want them blasting air at each other within the motherboard nor do you want them depriving the space between them of fresh air.

Also make sure you opened the vent slats near the CPU if you're using an air cooler for the CPU. The ASUS website has a large infographic on it here:http://www.asus.com/Motherboards/SABERTOOTH_Z87/
("Thermal Armor with Flow Valve", click the "Flow Valve" tab that is located in the top-right of the big picture here)