Buckingham is right about the 4 foot drop. Have you ever seen the 'assembly lines' our packages go through to get sorted and out to the planes? It would just make you wince! I've become a big believer in overpacking and double-boxing. Much worse than UPS, IMO, is FedexGround!! They've destroyed no less than six separte shipments I've either sent or received, and most were well-packed. I've had to deal with claims with them, and let me tell you they make it as difficult as possible to pursue. That is the job of their claims handlers in my experience. The only way you are going to get you claim paid is to be utterly relentless. They are counting on you giving up. With my claim I actually filed a claim with the Better Business Bureau, which is when they finally paid it! Mine was an $800 subwoofer which was utterly destroyed by FedexGround. The box looked like it had been through a war! If you want to get paid, don't give up, and continuously express your outrage (assuming that you believe it is justified...if the speakers were actually poorly packed then it probably is not worth the effort, and you have to decide wheter it is morally right to pursue it further). As Buckingham suggests, with more fragile items it is best to go with an air service, rather than ground. In the end it is worth the extra cost simply in piece of mind! For economy and effeciency I have not found a better alternative to USPS Priority Mail. They have never damaged a package I've sent or received. Unfortunately their size limits prohibit a package the size of your speakers.
Good luck!
Good luck!