Ebay selling my missing amplifier

if you contact the seller telling him it's yours, you are giving him a warning essentially to pull it from ebay and cover his tracks. Use your knowledge to your advantage. You don’t catch a criminal by emailing him that you are onto him

If you collected a insurance payment from the loss, it isn’t yours anymore, the amp belongs to the ins. Co.

if that is the case, just report it to them, they are the experts on recovering 

That's horrible, hope you get satisfaction.  Good luck!

Police report + court on all missing and spent assets and attorney fees + some extra...extra++ fees for not pressing criminal charges

This is not necessarily fraud. Cargo Largo specializes in re-selling lost shipments. Their whole business model is buying lost UPS / Fedex / etc packages at auction for pennies on the dollar and re-selling those items.

I suspect that they are obligated to give you back your amp, if you can prove you are the rightful owner. Before going to the police (some folks here are real trigger happy), contact Cargo Largo directly. If I were a betting man, I expect you two can work it out.