Hi,
I can exclude some that I have already looked at.
1) The plain com.apple.ichat.plist
This does hold some info about the Saved and Recent Available and Away Messages but these tend to be old ones (it shows some on Mine that have been deleted from the Away list in particular).
In the .plist there is nothing about the "current iTunes playing' option.
2) the various "account" .plists.
The AIM one lists all the AIM and AIM valid Logins and this have reveal triangles when using Xcode to view that show the server and various Account settings in those.
These would be the Jabber, Yahoo and Subnet (for Bonjour) ones as well as the AIM one.
2) The com.apple.iChat.LSSharedFileList.plist used to be the one that held the Recent Items lists (both A/V chats and Text chats of all types but even this is not longer held here.
3) The logical one would seem to be com.apple.iChat.StatusMessages.plist but it is not.
It just holds the Current Available and Away messages with nothings about what is being played
The same applies to likely items in ~/Library/Containers/com.apple.ichat and com.apple.soagent
Some of the soagent ones are not Aliases that lead back to the ~/Library/Preferences ones but I have found nothing yet.
I did try using the Modified column and changing the setting to On and Off.
The com.apple.ichat.plist does seem to be the only one in the ~/Library/Preferences that changes.
When we were first doing this the info did not appear in the iChatAgent .plist as to the order.
It seems many settings don't show until they are changed.
One this I have noticed when I enable the settings for Current iTunes Playing it also sends up and Notification each time the Track changes.
I have an app to update here so I will look again later.
7:55 pm Wednesday; March 19, 2014
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad