Why don't you do your CPL first? You don't need a JAA PPL to start a JAA CPL course - it just needs to be issued by an ICAO member state.
Then you can add your ME rating to your JAA CPL - saves messing about and converting your PPL.....your JAA PPL will just become obsolete as soon as you get your CPL anyway. It will save you a bit of money.
If you really need to do the ME and IR first, then yes, you will need to convert it to a JAA PPL first.