I had one batch of drives that needed a firmware update. The drives
were all in USB cases, but to apply the firmware updates using the
vendor's utility I had to remove each drive from the USB case and
install in an old PC.
Yes, that sounds familiar :-)
I did manage to update a couple of Seagates here through USB with
hdparm, but it took a bit of trickery to figure out the right options
and to extract the actual firmware binary file from the manufacturer
downloadables.