How do I point Sonos to my music on an Airport Extreme connected hard drive? I am attempting to set up a music library to use on my wifi based Sonos system.  I have moved a copy of my iTunes music collection to an external USB 2.0 drive (Seagate FreeAgent GoFlex Drive) which is attached to the USB input on my AirPort Extreme (ac version).

On my MacAir, I can see the drive as a shared drive, and I can access all the files, including the music files.

In my Sonos setup, I have tried to identify the drive and files as the source of my music.  In identifying the device type, I have chosen

on a networked device such as a networked attached storage (NAS) drive


I am then prompted to 

Type the path to your networked share:


Examples are given, such as

\\MyNetworkedStorage\Shared\Music


But what is my path?  When I look at the description in Finder on the MacAir, all I see is Server followed by 

afp://MyName's AirPort Extreme._afpovertcp._tcp.local/MAC FREE/free agent backup/FreeAgent GoFlex Drive/iTunes/iTunes Music


Clearly the formatting is different from the example paths offered. When I enter this entire string (and several shortened modifications), the dialog box does not recognize the string at all and no Next button appears.

When I modify the string and remove afp:, the Next button does appear. This is followed by a login for the Airport Express (which I input), but when I go to the next screen, I get the message 

The computer [the address I put in follows] cannot be found.

How do I show Sonos where the networked drive and files are?
A Sonos requires that shared libraries are accessed over CIFS/SMB. From your path it looks like this link is for a share over AFP. Can you find a link for the SMB share from the airport extreme ? Looking at the Airport Extreme docs it seems that if you have an HFS formatted disk mounted then it will share over AFP and SMB 

you could try (just a guess) as a link 


  \MyName's Airport Extreme._smb._tcp.local\MAC FREE\free agent backup\FreeAgent GoFlex


You might also consider removing spaces in the paths as these tend to cause pain if the software is not expecting them