Thanks for your reply.
In the same computer, ML 10.8.5 worked with the airport card without a hitch. In Mavericks, weird stuff happened. I tried importing my ML Networking Interface into Mavericks with proper terminal commands from eep.
ML and Mavericks have the same support for WiFi cards. I don't know what you mean by "importing my ML Networking Interface into Mavericks," but it doesn't sound a like a good idea.
It installed correctly but it shuts off Wi-Fi function. In Mavericks, I can only have either Wi-Fi or Marvell Yukon Lan. If Both kexts are loaded, only LAN works and Wi-Fi showed up in network setting and I could not turn it on through network setting.
Key is not messing with the system kexts IO80211Family.kext or IONetworkingFamily.kext as it is unnecessary to replace/patch these kexts and doing so just leads to problems.
Going through my DSDT.aml, I could not locate the Airpot Atheros 9380 at all. Yet, it clearly displayed in the IORegistry. I was hoping that if it showed up in DSDT.aml, maybe some patch might work.
Use the information in the ioreg to find it in your DSDT (eg. node in ioreg corresponds to node in DSDT).
WOuld changing SMBios to MacPro 3.1 make a difference?
I don't think smbios matters for your case.
If I try your NullEthernet Kext with SSDT, if it does not work, can I just uninstall the kext and delete the SSDT and back to square one? I am desperate to try anything as long as it does not give me serious KP that I cannot fix it myself.
Yes. And BTW, there is no such thing as a "serious KP" that cannot be fixed provided you know what you changed to cause it.