Complete WiFi Sync Failure iPhone

Hello everyone,

I think I've literally exhausted every possible option with regard to my issue, so I thought someone here might have a suggestion for something I may have missed.

Here's the problem:

My iPhone 4S refuses to WiFi sync (automatically or manually) because it seems that it cannot locate my iMac. Everytime I try to manually sync over WiFi by going to Settings/General/iTunes WiFi Sync, I can press the button -- IT IS NOT GREYED OUT -- but the sync constantly says "LOOKING FOR ******* iMac and then timesout. I cannot see the device in the iTunes sidebar unless I plug in via USB -- as soon as I unplug, my iPhone disappears.

The oddest thing is, when I first got the phone, it worked perfectly -- and then it randomly stopped -- and has never worked again.

Here's my setup:

27" iMac (Late 2009) running OS X Lion version 10.7.3

Airport Extreme running firmware 7.6.1 with a/b/g/n bands enabled -- secured with WPA2 Personal.

iPhone 4S 32GB running iOS 5.1 

Here's what I've tried so far:

The basics:

Making sure the WiFi Sync box is checked.

Made sure both devices are connected to the same WiFi network.

Uncheking and re-checking the Wifi Sync box and re-syncing.

Making sure that "Open iTunes when this device is connected" is checked.

Made sure that "Prevent iDevices from syncing automatically" is unchecked.

Restart all devices (i.e. iPhone, iMac, Airport).

Hard Reset iPhone.

I have also tried:

Restoring the iPhone from a backup.

Restoring the iPhone as a new device.

Deleting all existing iPhone backups.

Wiping the Airport Extreme and re-configuring.

Using the "restart your Airport from your iPhone through Airport Utility" method that has been suggested.

Hardcoding IP's for both my iMac and iPhone into the Airport Extreme.

Disabiling wireless security on the Airport.

Disabling Mac OS X firewall.

Port forwarding the necessary ports.

Uninstalling iTunes using the necessary terminal commands and reinstalling.

Opening the ports Apple suggests in the WiFi Sync support article on both the Airport and the OS X firewall.

Some notes:

I know my iPhone and iMac are aware of one another because the Sync Now button isn't greyed out. I can also PING my iPhone from my iMac using the Network Utility successfully.

Two other family members have 4S's in my home on the same network that sync with Windows PC's without issue. Whatever this is, it's isolated to my iMac.

About the only thing I haven't tried is completely restoring my iMac -- which I'm hoping I won't have to do.

Any suggestions anyone may have are greatly appreciated! :-)

Thanks in advance to any and all responders!!