There was a Virus C mod for the Z3ta released unofficially a couple months ago. It took some waveforms from the virus to get a virus-ish sound. But the only draw back was they were all arped and sounded really crap when used without them.
The virus really kicks the z3ta`s ass. Its not nearly as fat and as said before the filters are nothing like each other with the virus coming out on top.
But the z3ta is a good software synth to have, defiantly worth having on your system..
