Nice! Now audio meter and audio remote shot work properly.
But, i don't understand. If audio_thresholds does not exist in 500D, what is 0xFF4631F4?
Edit (add):
Btw, there is audio_thresholds in ML for 500D non-unified version, pointed to 0xFF48E58C (firmware 1.1.0), and audio features work with no problems...
Edit (again):
Changed audio_thresholds address to 0xFF48E6AC. It gives similar effect to your fix, and audio remote shot works with this address...