sadly I don't think you will be able to recover from this. The 300X series are very tricky (in terms of hacking in comparrison to the 100X & 200X).
Basically, once you are bricked there is no going back. MAYBE if you can access your Flash0 you could overwrite your .prx's back to default (assuming you have backups, or could find them online).
Best of luck to you. I will see what I can do.