Since the shipper buys the insurance from UPS he is the insured party and he has to file the claim with UPS, which is why they sent it back to him. Not that that does any good because UPS and other shippers are notoriously bad about paying for damage.
Here is what Audiogon has to say about your situation in the Support Center:
What if an item is damaged in shipping?
If an item is damaged in shipping, you should contact the seller immediately so that a Damage Claim is filed.
***The responsibility of pursuing a Damage Claim is solely with the seller,***
however, you will need to cooperate with the with the seller and the shipping company in any manner requestsed. Often, the shipping company will come back to pick it up, or inspect the package in your home.
Keep all of the packing materials exactly as you received it.
Do not attempt to use the item or plug it in, which may result in further damage.
Do not attempt to disassemble or repair the item unless the seller first agrees.
Take photos of the item and the packing materials as soon as possible.
If a seller and a buyer cannot agree on a course of action to follow, a Dispute may be filed with Audiogon here.
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It looks like you're going to have to file a Dispute with Audiogon.
Here is what Audiogon has to say about your situation in the Support Center:
What if an item is damaged in shipping?
If an item is damaged in shipping, you should contact the seller immediately so that a Damage Claim is filed.
***The responsibility of pursuing a Damage Claim is solely with the seller,***
however, you will need to cooperate with the with the seller and the shipping company in any manner requestsed. Often, the shipping company will come back to pick it up, or inspect the package in your home.
Keep all of the packing materials exactly as you received it.
Do not attempt to use the item or plug it in, which may result in further damage.
Do not attempt to disassemble or repair the item unless the seller first agrees.
Take photos of the item and the packing materials as soon as possible.
If a seller and a buyer cannot agree on a course of action to follow, a Dispute may be filed with Audiogon here.
//////////
It looks like you're going to have to file a Dispute with Audiogon.