Tom has pretty much got it.
I work for Customs, and can give a little more info. While I personally don't mess with duties anymore, I remember a little.
I assume you will not be picking the speakers up at the airport? If not, you will have to hire a freight forwarder (carrier). The invoice/manifest should be completed by the shipper (or sender of the speakers).
Once Customs clears your goods, the carrier will then pick up your speakers for delivery. I did look up the duty charge and you will have to pay a 4.9% duty charge. You may have the option to pay the fee in advance with the carrier you hire, or possibly pay the duty charge when the carrier delivers them.
Contact the shipper (sender) and make sure the invoice and manifest will accompany the goods prior to shipping to the States, as this will save you some hassle.
While this is the "legal and correct" way of importing, some do things "differently".
Mark