Remember- If one gets "lost"- you are hosed. The shipper will only pay the cost of one speaker, even if it's impossible to replace just the one for any reason.
It happened to me- the speakers I shipped arrived safely at the FedEX hub in Memphis, and only one left. The other disappeared IN THE HUB and FedEx never found it.
I could not buy one to replace it (that particular model was no longer made) so my buyer, naturally, wanted all his money back. I argued forever with FedEx but to no avail- they said you have one good speaker, and one's gone- so we owe you for one.
And no, you can't insure each speaker for twice it's value to cover this- FedEx demands receipts and checks the value, so the amount you insure it for is really not valid if it's for more than a single speaker.
I refunded the buyers total purchase price and let him keep the one speaker that made it there.
Lesson learned? Listen to FatParrot- strap them together on a skid and ship via freight.