I think I did it by looking at systemctl list-units --type device. It occurs to me now though that sound.target is probably a better choice. With that in place:
$ systemctl list-dependencies sys-devices-pci0000:00-0000:00:08.1-0000:07:00.6-sound-card1-controlC1.device
sys-devices-pci0000:00-0000:00:08.1-0000:07:00.6-sound-card1-controlC1.device
● └─sound.target
○ └─configure-sound-leds.service