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.