3.42A will power a Pi..possibly a Pi and the Amp2 but note the warning from HiFi Berry...
Try a powered USB hub between the Pi and the USB drive.
https://www.hifiberry.com/shop/boards/hifiberry-amp2/
Quote:The Amp2 integrated voltage converter is powerful enough to power even the new Raspberry Pi 4. Just note that it is not designed to power additional power-hungry USB devices or other hardware. There isn’t a problem with low-power devices like mice, keyboards and similar. There might be even enough power for external hard disks, but the system might become unstable if too much additional current is drawn from the USB boards or the 5V rail on the GPIOs.
Try a powered USB hub between the Pi and the USB drive.
https://www.hifiberry.com/shop/boards/hifiberry-amp2/
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bob
bob