It's PCI and PCIe x16.. The x4's, and x1's don't really matter.
PCI is used for sound cards, PCIe x16 is used for graphics cards.
SLI is a waste, honestly, 1 PCIe x16 slot is sufficient. For PCI it doesn't really matter that much either, 3 - 4 is fine though. Just because your motherboard has 2 PCIe x16 slots doesn't mean it's SLI or CF, however.