I can't find any plugin for winzix. I have found an open source version of the umpacker, but I don't know how to make a plugin for this myself. Anyone up to the job ??
Use the 3rd party command line utility you can find linked on Wikipedia and create a MultiArc addon if you really need to. I could do that but I have no desires to help proliferating junk wrapper formats.
This is what Kaspersky says about Winzix:
not-a-virus:FraudTool.Win32.WinZix.a