it's this easy!
buy a pair of 6x4 2/3way speakers from any car audio outlet...
I used the JBL ($100 strathfield car radio) as they provide a little more depth than most others...
remove the original speaker/plate from dash
take to it with a jig/metal saw or even a hacksaw... cut away the speaker and brace leaving only the bracket..
then mount new speaker to bracket and re-install.. DONE!
and all it costs is $100 and 25mins of your time