So far as I can tell, the speakers are under UPS's maximum shipping weight (68kg), but heavy enough that they match up with UPS "special guidelines" for heavy packages (>31.5kg), which requires more sophisticated packaging, like a double-thickness cardboard box.
This is just a quick comment to say I once shipped a Subaru WRX 5-speed transmission through UPS from New York to Rhode Island. It was not doubled-boxed, though I used copious amounts of expanding foam. It was accepted and delivered with no issues.
Conversely, I could call a commercial freight shipper and probably end up spending a lot more money, but then maybe they would do a whole shipping pallet, shrinkwrap and straps and such, which might maybe do better in a cross-country adventure?
We routinely ship loose cartons with YRC, ODFL, R+L, and other LTL carriers. These are items that are outside the dimensions UPS or FedEx accepts. We have contracts with these carriers that take something like 80% off their published rates. But, services do exist that also have access to these rates, add a markup, and then sell to you. One such service I'm familiar with is freightquote.com
. I'm sure there are plenty others.