SJNobles,
I've done both: passing through the individual devices, and passing through an entire USB card to the machine, the latter of which I've found more reliable. With the XBMC VMs, I've had some issues with wireless keyboards going offline, most likely from them sleeping, and ESXi disconnecting them (this is only conjecture, I haven't investigated much further).
My go-to motherboard has been the ASRock 970 Extreme3 or the Gigabyte GA-970A-UD3. You can see my lab, and full information on my builds at http://thehomeserverblog.com