I urge you to take them to a UPS store and let them package and ship them. It will likely cost more but if you want to ensure an undamaged shipment or at least an insured shipment that you can "collect" on that is the route to go. I had a nightmare shipping a pair of Spendor S100 to California from Rochester NY. A friend runs a registered Fedex shipping store. He packaged the speakers exactly the same way a speaker manufacturer packages speakers for shipping. Double boxed, 3" foam cushions in each corner and along all edges. Labeled correctly as "this end up", "heavy", with the total mass of each package. A week later the buyer in California sent me pictures of the speakers upon arrival. One box was destroyed as was the top front edge of the speaker in that box. Some internal damage along with the damage to the wood cost $600 to repair. I was assured if I would refund the buyer's cost of repairs I would receive those monies back after filing a claim with Fedex. The claim has been denied twice and there is no positive outlook for me getting my $600. The only other thing the shipper could have done was strap the boxes to a pallet with metal bands from both sides. In hindsight that would have been the best shot at getting those speakers to their destination without damage. Even then, there is risk. I assumed that is why one pays for insurance. If the shipping company deems you did not properly package the item(s) then you at fault, not them. Next time I go to UPS, or some other shipper, and let them do it all. 100% responsibility on them.
Packing & Shipping Large/Heavy Speakers
I have a pair of Legacy Whisper XDS's I'm wanting to sell. They measure 63x17x13 and probably weigh about 200lbs (or more), so extremely large. Most of the advice I've read is simply to crate them on a pallet and then ship freight; but how to go about that? I know for freight shipping there are websites to get quotes, but it's really the packing aspect I'm concerned about having never tried to pack anything this large.