rashidalsaleh,
One question you have to ask yourself is "where am I going to work?"
There is no point in the FAA licence if you intend to work in Europe.
If you can't work in Europe, then the EASA licence isn't much use.
What do the Omani Authorities stipulate?
Yes, if you convert your Australian CPL to an FAA one, plus convert the IR, if you do your ATPL subjects, you'll be able to get an ATPL when you have the hours, pass the check etc.
At the moment, you have a CPL. When you get the hours + pass an LST (licence skills test) you'll get the ATPL.
If you pass the ATPL subjects now, you'll still hold a CPL.
If you're wondering how to phrase it on a CV.
CPL xxx hours
IR expires xx/xx/2012
ATPL theory subjects completed date XX
In most regions outside of Europe, they won't understand what fATPL means.