Since 'ifconfig -a' is not showing your wifi device (wlan0) then pretty much your wifi is not started up for some reason. When you modprobe the ath9k driver what is 'dmesg' saying?
I don't have too much experience with Atheros but the following thread
seems like is related to your issue. Anyhow, when you load the driver is '/proc/net/wireless' present on the system? If not, then the driver is not doing its job even-though it may be modprobed in.
In the thread posted above the issue is related to gentoo's kernel config, so it is a good idea to re-check that too.
Hope that helps.