Things you can do to make your shipping experience as boring and uneventful as possible, (which includes paying as little as possible, and not worrying whether they are going to make their safe and sound!) are:
One, put your speakers on a pallet and ship them as freight. This means that the shipping companies can use a forklift (which is relatively safe due to the pallet), and your speakers will (usually) be kept in an upright position.
Two, have the shipping company put a layer of at least double thick cardboard around the speakers on all sides and top. Then have them shrinkwrap the package to the pallet. (Note: my speakers arrived save and sound, but my buyer did note that there were a couple of good sized dings in the cardbroad armoring that might have penetrated the speaker box had it not been there!)
Three, deliver the speakers yourself to the shipping terminal, and have them shipped to closest shipping terminal to your destination. (This will mean dropping off and picking up speakers by your and the recepient, but it will save you time and money.)
Four, bite the bullet and pay for insurance though. Typically the cost is around 3% of the insurance amount.
I recommend the following shipping company.
They were very helpful and were (relatively) cheap.
Navis Pack and ShipFYI, I recently used them to ship my Revel Studio speakers from San Jose, CA to Denver, Co. The total cost was about $616, if memory serves. And, $150 of that was for the $5,000.00 worth of insurance. The total weight of everything, including the speakers, pallet and extra cardboard was about 500 pounds, so I think that is in the same ballpark as your situation.
Good Luck!