Best shipping companies

Packed in original carton they weigh around 185 lbs each

 Have them shrink wrapped and palletized and ship them freight. 

Agree with winoguy. You can also save a lot of money if the seller drops off the speakers at the freight terminal at a major airport and the buyer picks them up at the freight terminal on the other end. Most of the cost is the local delivery between terminal and local address. 

@referee1 I have shipped a few sets of speakers across the country and have never had an issue.  I take the time to pack them like this.  Materials cost about $100 and worth very penny.  Requires a skillsaw and a drill.