This was my solution:

1. Shared the 2nd PC's \Users\<user>\AppData\Roaming\Microsoft\eHome\DvdInfoCache folder
2. Added this shared folder under YammmConfig Metadata Additional Folders
3. Entered an admin user/password for 2nd PC under YammmConfig Library Network credentials
Watched the shared folder on the 2nd PC and saw YAMMM000-xxxxxxxx.xml files added to it.
Pulled up MC on the 2nd PC, gave it a long few minutes and I got the cover art, etc.
Even though my 2nd PC's share was read/write by everyone, I still needed the credentials for YAMMM to push the files to the shared folder. If I want to do a 3rd PC (I do) I suspect I'll need the same user/password on all PCs as there is only one credential entry possible.
Couldn't find this anywhere, so I figured I'd share it.