Start by going to your local big box retail store and asking them for some large sheets of cardboard from a flat panel TV or appliance and also see if they have some heavy duty cardboard corner pieces that are used to ship fridges safely. Wrap the entire speakers with several layers of cheap cellophane wrap (Saran wrap) to protect the surfaces of the speakers. Attach the cardboard corners to all edges of the speakers and make a box out of the sheets of cardboard to use as your "inner" shipping box, then surround that box with 2" of white styrafoam (available from your local home improvement store for $10 per 4X8 sheet) and then make your final outside box around the styrafoam. It sounds like a lot of work, but if they're not packed in this manner, FedEx or UPS will deny any damage claim due to "insufficient packing".
Dave
Dave