The ISO-DAC & ISO-SPDIF devices also operate as an ISO-HUB with 4 isolated USB ports which can be used in many ways (the rightmost USB port can only be used for 5v power injection - see below)
You can connect any USB device into the ports - another USB DAC or a USB storage device stick or SSD drive containing audio files.
The USB storage appears as a drive, like any other storage device & the audio files may be played back off this drive. This provides isolation & reforming of the audio file data being read off the drive.
5V power is needed on the USB ports to power these USB storage devices. By injecting 5V power into the rightmost USB port it is then available on all the other ports. I can provide a cable which has a USB type A connector at one end (which plugs into the rightmost of the 4 USB ports) & the other end has a 2.1mm socket which accepts a 2.1mm DC plug with 5V on it. In this way, you determine the quality of 5V power you want to inject here. It can be the same 5V supply as used to charge the ISO device.
I'll put together a graphic showing how the 5V supply can be fed into the rightmost of the USB ports & the USB charger cable plugged into another USB port & 5V fed back to the DC input socket on the ISO device. In this way the one 5V supply provides power on the USB ports & also charges the internal battery
Only the back of ISO-HUB is shown but this is the same power configuration for ISO-SPDIF & ISO-DAC providing 5V on the USB output ports on these ISO devices if the ISO-HUB function is being used.
Remember that any USB devices being powered from the USB ports draw current & the PS powering the ISO-PS internal battery chargers must supply more output current than the total current needed by these powered devices.
There are still 2 free USB output ports into which any USB device can be plugged - USB stick, USB drive or another USB audio device, DAC or SPDIF.