Question I Have Never Seen Before?

Call your local crating company they usually carry double walled boxes. But beware, I would not ship something like that unless they are small. Thats just crazy and risky.

I would buy a roll of shrink wrap and wrap the living crap out of them and put the shipping label on it before tryin to do boxes. I have done that before.

I shipped heavy Reference 3As (in boxes) by Greyhound once. Worked well and was cheaper than FED/EX or UPS.

Call the speaker maker and ask to purchase boxes only.

Shrink wrap, corner pieces on all 4 sides then taped around. Cardboard over shrink on all 6 sides.

If smallish or monitors, (two in one box) face the drivers towards one another.

Then Bub-bub-bub-bububble wrap it till it bounces.

Then strap 'em to a sturdy 4 way oak pallett fore and aft, and as well side to side, standing upright! That way they'll arrive together, and strapped to the pallett, nothing can be set onto them.

Aside from a Shrike missle or termites, you'll be fine!