They will almost certainly open the box, so I think you're doing yourself more harm than good by packing it so well, considering that it will only remain packed until it gets to the first airport.

Have you considered something like a Rubbermaid Action Packer? They're one inch less than the linear maximum of 62" for checked luggage, and most likely the machine fits fine with adequate padding.

I have checked in both an espresso machine and a stand mixer in their original packaging, and both were fine but both were also opened.