In order to use an external device as the source for Music on Hold, you will need to purchase an audio-to-USB sound card adapter. Here are two tested options that we know work with Switchvox:
Turtle Beach Amigo II USB sound card (TBS-1155-01)
Sabrent AU-MMSA USB Sound Card Adapter
Plug the device into the Switchvox USB port
Log in to your Admin account and navigate to Tools>Music On Hold>Groups Tab
Now select the Group Settings tab and set the Default System Group to external and save the group settings.
After performing a software restart the PBX will begin using the Music on Hold from the external device