There are multitudes of Packaging providers. Have you though of an "in-house" system as a part of your payroll function?
Otherwise try
www.smartsalary.com.au A sydney based organisation a heavy player especially in the public health industry as well as others.
MacMillan Shakespeare(City) A Melbourne based company - happy to discuss further offline
Remunerator (Hawthorn) A Melbourne based company
As I said there are multiple choices to make, just a thought you may find that employees will get more for their buck if you look at maybe a smaller or 'up and coming' organisation where their maybe more room to move and negotiation.