I have Z3100 24" with MacPro, connected via ethernet. I downloaded both printer driver and firmware, and updated my printer without a hitch. The firmware update took less than 10 minutes, printer started up by itself, and functioning perfectly.
I am in process of re-calibrating and profiling paper
Pay attentions to what you are downloading, select proper OS, Language, etc. Once it start updating the firmware, leave alone both computer and printer until it completes.