the other two slots are buried inside the laptop and require an almost complete disassembly to reach them which voids the warranty as well -I know, it sucks. Anyway, 32GB is really a massive overkill for any consumer application unless you are a professional that knows exactly how he is going to fill them. I would suggest going for a 16GB solution, or 24 if you really think you will need them.
ASUS G750JX -- i7-4700 - 16GB - 128GB 840 PRO SSD + 1TB HDD - Nvidia GTX 770M - 120Hz 3D glossy display