File Location + WMP 11 Cfg
The files apparently must be located in the hierarchy of the Shared Music folder. I'm not sure if the Yamaha is hard-coded (in BIOS) to specifically search out a folder by that name, or if it's smart enough to reference the Registry path. If the latter, then the location can be changed. I'm investigating that now.
As for WMP 11 (which includes the requisite Windows Media Connect; pre-XP operating systems need not apply):
Under Sync, click the little downward arrow, then choose More Options > Library > Configure Sharing. Engage the Share My Media To checkbox, then click the [Settings] button at the right. Give your music folder a share name (the Yamaha will display this on a TV), then engage the Music checkbox. Also engage the Allow new devices and computers automatically checkbox. Click [OK] as many times as needed and reboot.
I've since Googled to learn how to change the Shared Music folder path in the Windows Registry (HKLM/Software/Microsoft/Windows/CurrentVersion/Explorer/Shell Folders[Common Music]), but at the moment it's not specifically named Shared Music, so the Yamaha isn't seeing it.