Do not donwgrade the config, it will get corrupted.
I have done it twice and both times the config got corrupted, for example it becomes impossible to change extension numbers, you cannot add IP Extensions manually and a lot of other not so funny things.
To get to your question, set the working path for the bin files to the folder were the 9.0.4 bin files are.
Once again, do not downgrade the config! Export those items which can be exported, after downgrade factory default the unit and rebuild te config from there.
It really save you a lot of hours fixing things which cannot be fixed.