as far as the audio is concerned, providing you can prove it was in the vehicle when it was towed, then whichever company, that dealt with it afterwards, has a duty of care, for you belongings.
A friend smashed his saab up a few years ago ,and the police aranged a local company to recover the vehicle and lock it in a compound(middle of the night) when he went next day to remove his stereo and personal belongings , you guessed it ,all gone.
he kicked up stink with them and they said somebody must have stolen them from the compound, so not there problem.
he went to the police and complained that they had been stolen from his vehicle whilst in there approved recovery agents care and very quickly was contacted by the recovery company, with a cash offer.
furthermore when the FIL had his accident 4 months ago, we had to go to the compound where the car had been taken to remove his items and all personal belongings had been removed and were stored in lockers,plus had been , logged in and signed as inspected by the driver and his boss.
most modern companies will have a paper trail to follow.
if they argue the toss report the items as stolen and kick up a fuss.