Sounds like you should talk to the adjuster after you make the list of things you will be removing. If the item doesn't add value, then you would not lose anything removing it. So the head unit doesn't add any value then taking it out doesn't remove any value. If something adds $50 in value but costs $500, then remove it and take the $50 hit to the overall value.
Another option is to talk to your insurance and work with them on value/parts. They may be willing to pay you for anything you've added to be covered (like aftermarket parts you added to your policy) and then get their money back from the other insurance company.
If none of that fits for you, the lawyer option may help. I do not know if they really get into the vehicle value discussion much (didn't back the last time I had an accident but that was many years ago).
Hope you get this resolved to your satisfaction!