BAX Global is who I use for large items like speakers, they do a very good job. FedEX freight is also good, though they have a size/weight limit. BAX will ship damn near anything, and even pick up right at your door (though this costs more). I shipped a 330 pound pair of speakers cross-country with BAX, fully insured, and if I remember it cost the buyer something like $400 or so.
www.baxglobal.com
www.baxglobal.com