Using libusb sane happily detects the scanner and root can use it. The only trick here is using sane-find-scanner to get the vendor and device ids. You add these two numbers (hex numbers) to the “usb” line in /etc/sane/dll.conf. Once you do that root can use the scanner.
Getting any other user to use the device is more challenging. You need to use hotplug and libsane comes with scripts that should set the permissions to root:scanner for you. Oh, yeah, I forgot to mention that the Debian packages setup stuff to use root:scanner so any user you want to have access to the scanner should be added to the scanner group. However, the hotplug script that comes with libsane reads from a database of known devices. I”m not exactly sure why this is…I suppose so you can have different access controls for different scanners. Anyhow, you need to add the vendor ID and device IDs to /etc/sane/hotplug/libsane.db (I think that was the file). Now, finally, once you have done that the scanner will be accessible to anyone in the “scanner” group (you”ll have to relogin the user of course and you may have to replugin your cx-4600 to force the script to be run).