McIntosh Double Box?

Def NOT. It's double boxed for a reason and there are countless examples of broken faceplates with Mac product due to people cutting corners packaging a piece when shipping it. Additionally, if you do ship it in a single box and even if you insure it, if it gets damaged chances are high the insurance won't cover it as they want photos of the packaging etc, and they'll figure out it wasn't packed properly. 

If you're short of space for the cross country drive, then ship the double boxed C2700 rather than drive it.  Ground ship it and require a signature.

Good advice above. As to the question of whether the double box is necessary for shipping safety, the Mc boxes are fine for lighter gear like a tuner or some preamps, but the heavier gear needs a second box for protection in worst cases. 

Usually their equipment bolts to an inner rigid bottom piece that fits inside the inner box, that is the primary method of preventing movement.

KEEP that outer box, McIntosh would never ship it without it, and UPS REQUIRES Double Boxing for any insurance claim.

You could cut the outer box, flatten it, then if ever needed, tape the heck out of it.

If you want, sell it, or toss it, or ask a friend with space to keep it for you. Invite them to visit you, bring the damn box!

Or, in the future, McIntosh will make and sell you an outer box, and ship it to you, for $____. I paid $75. for a box I bought many years ago.

Another possible solution is only use the inner box for the equipment & then put other things you’re bringing in the car in the outer box assuming both boxes can fit by making room for it with the stuff you put inside it.