shipping boxes for heavy electronics

Elizazbeth is correct. Multiple boxes, plenty of thick foam. I just shipped out my old Carys with the original packing, which included very thick foam, and 3 (yes 3!) strong thick cardboard boxes. However, I have heard that FedEX an UPS can refuse to pay claims if the original packing is not used, or if you don't let them do the packing. So Maplegroves suggestion about using a wood crate or pallet is also a very good suggestion.

As noted above, you should see if you can buy a box from Parasound.

Another option is to contact a packing company like the Box Stop. You should ask the Box Stop (or other similar company in your area) for their opinion on the best way to pack and ship your unit. This will ensure your amplifier gets packed correctly. For example, see http://boxstop.biz/

I have used them several times and they are very good. Most likely, they will use a double box, include bubble wrap and/or foam, as needed, to protect your amplifier. The use of a professional packing company will help ensure your amplifier get delivered safely. The cost for this professional packing is reasonable and is recommended because of units weight.

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Buy the box from Parasound. Whatever they charge will be worth it.

Liz's instructions are spot-on. Follow her instructions and you'll have a bomb-proof box. I've done it the same way dozens of times and I've never had an issue or a damaged item.

Professional packers are good, but very expensive compared to doing it Liz's way yourself.
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Elizabeth is right. However, for best result you need padding between both boxes. Logic does wonders. I've done many. Logic didn't always work with other issues, though.

At some point you need to use wood/plywood on a pallet to insure safe transit. The big 3, usps, ups, fedex have a poor record shipping our expensive and cherished audio components. Good luck collecting for damages also. I have had a couple of nightmares via UPS, they delivered a set of speakers to Florida and left them out in the open to soak up the afternoon thunderstorm. The gorgeous finish on the monitors was trashed, cones soaked- a total loss. They tried to blame me saying they were poorly packed. I got $400- for $2k speakers.
If you want it to get there safely, go freight.