I have bought several McIntosh units in the past 10 years. There is no McIntosh dealer within 200 miles of me - plus - I can't afford the new units.
So, I have had to have them shipped to me.
To me, Audio Classics is the best. I had a MC2255 that needed repair. They sent me a box. It cost $110.00. I was a little taken aback at the price, but when I received the box, I understood why. It was a TRIPLE box - with wood on the bottom with screws to hold the amp in place!!!
I have 16 McIntosh units that I have kept - I have refused to accept four or five due to shipping damage. One man took an amp (still in the wood case) to FedEx and asked them to package it. The unit arrived in terrible condition. I refused to accept delivery. The seller said he thought a shipper like FedEx would know how to ship electronics - NO WAY did they have any concept of an 85 pound unit with a glass front would survive!!!
One gentleman used an original McIntosh box - but it was about 20 years old. Remember - cardboard is just thick paper. Over time it will absorb moisture and lose its rigidity. That happened to the MC2255 he sent me. He had put it properly in the box - but the box was old and the MC2255 arrived with a broken face plate. My first reaction was to refuse to accept the unit - BUT - I could trace the provenance of this particular unit back to Apogee speaker company. It was worth it to me to keep the unit and find a replacement face plate - which was difficult at that time since NO ONE would admit to having any. Finally two showed up on Ebay - I bought both. I have four MC2255s, and with that many identical units, there is a chance that I might make a mistake and break another face plate - if so, I have a spare.
I think someone earlier in this thread mentioned McIntosh using plywood in their boxes now. If so, that is a great step in the right direction.
But - for my money - even if they are more expensive - Audio Classics is the place to get your shipping boxes for McIntosh gear.
P.S. - Do NOT try to ship a McIntosh unit in the wood case. The case will NOT survive shipping with an amp in it - and the amp also may not survive!!!