guest555 :
6R1M01R3 :
There is no reason to plug the 2.0 connector from the case to a 3.0 header (not that you can) you can only plug the 2.0 usb from the case to the usb 2.0 header on the mobo.
is cooler master elite 430 (which has 2.0 usb ports in front) not compatible with the motherboard asus m5a97 r2.0 (which says it's usb 3.0)?
Your motherboard supports USB 3.0 yes. It however also has 3 connections on the side of the board that are USB 2.0 ports.
To answer your question you case
IS compatible with your motherboard.