If you cannot find the original cardboard boxes, and are unwilling to personally move them separately, then they can be shipped with a lot of bubble wrap and cardboard. I had mine shipped ~1000 miles via UPS with custom wrapping. First they were wrapped with thin plastic wrap (to guard against scratches), then bubble wrap, then cardboard boxes, then a thick layer of newspaper, then more bubble wrap, then more cardboard boxes. I say "boxes" because the packager didn't have boxes of the correct size, but found some of a similar size, but not long enough, and taped them together to create a box of the correct size.
After traveling across more than 1/2 of the USA, I was walking out to meet the UPS guy to tell him to be careful unloading them, when, to my horror, I heard 2 very loud "WHAAAAP" sounds. When I walked around the corner of my house, I saw my boxes laying on my driveway. The UPS guy looks at me quite self satisfied and says "big tarps, right?". I just winced and "no, expensive stereo speakers".
Knowing people who have worked at UPS, this was probably not the worst handling that they were subjected to. UPS pushes their workers hard so they do not have time to be careful (regardless of what you write on the packaging). They throw packages because it's faster than carrying them. Even the final delivery guy basically threw them out of the truck.
Anyway, long story, but that was about 10 years ago, the speakers were already 10 years old at the time, and they still work fine. Maybe I was lucky, but they do seem to have a very robust build quality.
