I think you'll find that generally, the heavier the string, the louder the volume. If you want to bring up the sound on the top three strings, you could try extra lights (e.g. D'Addario EJ15) on the bottom three (E,A,D,) and slightly heavier (e.g. D'Addario EJ26) on the G,B,E. Unfortunately, unless you can find someone who needs them the other way round, it might become a bit expensive!