How do I find the path for the hard drive connected to my router?

To find the path to enter into the Sonos controller... If you're on Windows, try taking your computer to the IP address of your router, preceded with \\ (for example, \\192.168.1.1) and browse through the folders until you find your music. Then you should be able to copy/paste the path in the Address Bar of the Explorer window into the Sonos controller software. If you're on a Mac, it's a little different. In the Finder, press Apple-K, which should bring up a dialog box to connect to a server. Put in the IP address of your router, preceded by smb:// (for example, smb://192.168.1.1). You will likely be presented with a new window listing the folder(s) available through your router. After selecting one, this will appear as a network hard drive on your desktop. Now, browse to the folder of your music, making note of what folders you're going through. Back in the Sonos software, you'll need to add a shared folder, and enter \\ip.add.re.ss\drivename\folder1\folder2\... (for example, \\192.168.1.1\usbdrive\itunes\music). If, for some reason, you're not able to access your router by going to its IP address in Windows Explorer or MacOS Finder, you may need to enable the file sharing capability in your router. You'll need to check the help files or manual for info on how to do that, as every router is a little different in how they implement it.

Thanks MikeV. Your detailed instructions were very helpful. I very much appreciate your response to Martin_19.

Here is How to find out the IP address of your router in Windows PC
Open Command Prompt.
Now, write the command given below.
Ipconfig
The IP address written beside Default Gateway in the output is your Router IP address.
Source:- http://merabheja.com/ip-address-of-your-router-in-windows/