Filing a claim with UPS is certain to result in a denied claim due to the grossly inadequate packing. In addition, the claim process will note that the packing included misused / misappropriated materials. Specifically, the seller utilized USPS Priority Mail tape (the blue tape with the eagle logo) on the internal packing. Use of this tape on other than USPS Priority Mail packages is a Federal offense. Keep that issue in your pocket for backup as you work with the seller.
Your next step should be to immediately open a "problem" case (select "resolve a problem" for this item in your items "won" list) with eBay for the following reason: "My item doesn't match the seller's description". This will start the clock with eBay and ultimately, with PayPal (which is owned by eBay). Do not attempt to resolve the issue solely via eBay messages or worse, via standard email. The problem needs to be addressed in an official and documented manner. Waiting for the seller to file a claim is only going to result in lost time for you. After the case is opened, you have two options: 1. Obtain a repair estimate yourself and ask for the seller to refund you the repair amount or 2. Return the amp for a full refund, including shipping costs, BOTH ways. If the seller is not willing to do either of the two, then you would pursue the issue with PayPal. Specifically, your payment is refunded in full and you may still be able to keep the item. Keeping the item after your payment has been refunded is not the honest thing to do, so, I would have the seller fund the return shipping costs and then return the amp to the seller.
Long story short, you did not receive the item in the condition described in the auction, and this was due entirely to the seller's gross negligence with packing. Good luck!