Try a common carrier or freight forwarding company. They are designed to ship heavy items like this. I would guess you would be in the $450 range for that kind of size and weight.
Selling Large Speakers - How to reduce shipping?
I'm selling my Thiel CS6 that weigh about 200lbs each in their original shipping boxes. I'm looking for help in finding an economical, safe and insured way to ship these speakers within the USA. Both UPS and FedEx have a limit of 150lbs for normal shipping although UPS offers a Freight service that I found to be very expensive ($1000-$1200 to ship from Michigan to Texas or California). The speakers are packed in their original boxes that are 23x17x56 and weigh about 200lbs each. Any suggestions out there? Thanks in advance. Steve