From what I can tell, the Orbi only supports Readyshare for printers through the USB port. Some have been able to get a USB external hard drive to work though.

Do you have the option to copy the 50 GB of music files onto your Mac’s hard drive?

Thanks for your reply. Yes the music also lives on the Mac in iTunes. I can listen to it on the computer that way, but never do since I have Sonos in that room. I usually turn the computer off when not using it so I assume Sonos could not see it there. I was hoping to avoid a big set up with a NAS like with the Time Capsule. I have spent time looking on line and seems like the USB attached to the router that the Sonos is connected to is doable but I am not in the computer industry and am looking for an inexpensive and simple option if possible. Should I call Sonos? Thx for your time and interest!

See my edit above. What model is your Orbi router?

It is an RBR50 with 2 satellites. I am not familiar with readyshare program.

I found this discussion on Netgear’s community forums: https://community.netgear.com/t5/Orbi/ORBI-USB-Hard-Drive-support/td-p/1756369

I set up my iTunes music library on my iMac to be accessible on the Sonos app. I keep my computer on at all times but have the display set to turn off using a hot corner. I know this option is not ideal if you prefer shutting down your Mac when not in use.

A cheap solution might be a Raspberry Pi Zero W that could easily host your USB music and connect to Sonos via SMB v1.

Thanks for your reply.. So I have read that, but am not familiar with Raspberry Pi (apparently many “models” or SMB v1. Is there an item that you can recommend on amazon as well as a simple tutorial or “how to” to set it up

I can recommend the Odroid HC 1 or 2(depending on the physical size of the hard drive you are going to use). I have both, one with a 2 tb drive for my PC backup and Acronis images and the other as a dedicated Sonos Nas. 
i really enjoyed seeing them up too. 
There’s a great video here that takes you through the process  

You can do the same with any Raspberry pi board but I like the neatness of the integration of the drive that these offered  

Amazon has a lot of options, the first isn’t the cheapest but it is well supported and has all you’ll likely need.

https://smile.amazon.com/CanaKit-Raspberry-Wireless-Complete-Starter/dp/B072N3X39J/ref=sr_1_4

This is a nice step up and provides wired Ethernet as well as more ports.

https://smile.amazon.com/CanaKit-Raspberry-Starter-32GB-Official/dp/B07VDGKXBH/ref=sr_1_6

Instructions here: https://stan-miller.livejournal.com/  or Live Journal

If you want an integrated drive there are a lot of options, I use a second board, same size as my Pi that holds an M.2 SSD stick. That avoids any hassles with spinning drives.