Shipping large speakers

I have a hot tip for you. Call Steve Title at Gateway Crate and Freight. He can arrange al this for you and the best part is that he can offer very inexpensive insurance. They even have a white glove service. 

Pallets and shrink wrap are indeed ideal.

Tell him Jim at Sounds Real Audio referred you. 

Strapping is much better than shrink wrap. 

Definitely strap the boxes and strap to the pallet. Actually, I shrink wrapped the boxes before strapping.
My buyer used Uship:
https://www.uship.com/
It worked out quite well.
Bob