I did the JAA ATPL exams in 2009 & at the time I held an Australian ATPL with 1600 hrs and no type rating.
Apart from the fact there are 14 ATPL JAA exams and only 7 Australian ATPL exams you can guarantee the JAA exams are more difficult as the extra papers call for extra/deeper knowledge. Not forgetting the extra expense
You have to complete an approved JAA theory course (unlike the Aussie system) Google is your friend
I was able to sit the exams in Perth, Western Australia.
Good luck