I've been trying to find the fine for not having a working emissions equipment on your car in Vic, after downloading a bunch of PDFs, including a gazette (dafunk?), still no answer.
BTW, I have a HKS Hi-Silent cat back on my R32 (standard/compliant cat), it's no where near quiet! It's probably 90dB when cold (not happy, damn HKS).
Might be my old age, but why would you want a loud arse car for street? Annoy everyone? Get headaches? I guess if you drive it for a few kms a year it doesn't matter.
tl;dr enjoy what you have, or get an X-force varex so you can control the [action]sound levels.