So, I bit the bullet and picked up a NAS device to offload AV files from my Mac.
Now I want iTunes to run from the network disk drive instead of needing to keep the Mac on all the time. It takes less juice :-)
I followed a couple of different walk-throughs:
The key point from the ARS article is this: If the drive is not mounted at boot time, iTunes will not play. It also won't sync to an iPad or other device.
Most overlooked setup detail
Key was to go into the "Users and Groups" control panel and select "Login Items".
Here you can navigate to shared network resources, and set them to mount at login.
The drives need to be mounted before iTunes is launched. iTunes did move my music library to the external device, and correctly updated the file location, but it just chokes when it tries to play.
I had to reboot the Mac to ensure that the drives were mounted before it would work.
So, now we can share iTunes to PCs wirelessly. But for other devices the story is not straightforward, the NAS device does not have iTunes' home sharing. So accessing these media resources will happen through a non-Apple app from the iPad unless it has been synced through the Mac.