I have shipped SoundLab speakers via Delta Air Cargo. SoundLab recommended them. While you do have to take your item to the airport and pick it up, they were not only less expensive than anything else I checked but they were fast.
Best Shipper for Large Packages
I just bought a set of speakers (110 pounds apiece) and had them shipped UPS. I thought this might work out since I could get them delivered in a set time frame (3 day service), and I had to take time off work to be there. The brand new boxes showed up today, and they had so many holes in them they looked like Bonnie and Clyde after the Feds got done with them. What shipping services have other people used with better results?