I always had this problem with Gentoo: I was not able to use the multimedia keys and also the mice only worked in front USB bus of my computer while in the rear not.
The fix was in the Linux Kernel, I incidentally discovered an important parameter in the USB settings ^-^
You usually use de EHCI driver for your 2.0 USB buses, however what about the 1.0 buses? it is said to use some specific drivers while the most important thing indeed is to enable a subparameter of the EHCI driver!!!
This parameters are:
translate root device