This is the Elbox adapter and driver right?
Using the 4xEIDE.driver the ZIP drive must be a slave for it to work properly. It doesn't seem to matter if it is set to slave on a channel where there's no master.
Also, the driver will automatically mount an inserted zip disk as a trackdisk device and call it dfx: depending on which unit it is. Mine's the secondary slave, unit 3, so it's mounted as df7: without me having to do anything.
This is all in the docs you get on the driver disk.
Dont have 2 or more dosdrivers for 1 ZIP drive, I've found it will crash the system. If you're using a dosdriver from aminet for the ZIP then do a assign dismount df6: or 7, and make sure none of your active CD dosdrivers are pointing at the unit where your ZIP drive is.