USB 3.0 and USB 2.0 motherboard headers compatibility

Basically they're physically incompatible on the motherboard side, but there's very little stopping a USB 2.0 device or connector being used with a USB 3.0 header with an appropriate adaptor - a quick google search reveals there's quite a few appropriate adaptors with a USB 3.0 female to USB 2.0 male adaptor.

If you want a USB type A Male to usb male header, for use with that PCI cards try this search. You should be able to plug in the header on the device side to the male header, and plug that right in.

So yes, physical incompatibility aside, USB 2.0's pin out is a subset of USB 3.0, and with the appropriate parts, you can, in fact, plug in a USB 2.0 plug into a USB 3.0 header on the motherboard.