Zu Defintion 1.5 vs Def IV

Who to use for shipping is a crap shoot. Freight, strapped to a pallet, would be best if you could swing the $$$. I believe that's how Zu is going to ship your Def 4's. I would make sure to take plenty of photos during packing them up showing them in the custom foam enclosure. FWIW, I sent my Def 3's back to Zu with UPS ground without issues.
By the way, what color did you order your 4's?

My 1.5s are red matte. Not Ferrari red, rather Mercedes "Mars" red. My 4s are natural maple. Light and beachy like our home. My (5years ago) 1.5s came on a pallet because Zus packaging was the pits. I could never send my 1.5s back in them unless they were strapped to a pallet. That's why (doing it backwards, but less expensive) I'll send my 1.5s back in the same box of my 4s. Sean says they will fit like a glove and not to worry. Christian says I should be seeing these babies around mid February...sweet

I sent my Def 1.9s and my original pair of Def 2s to Zu using FEDEX ground without a problem. That is what Zu recommended and what Zu used to send me all but my Def 4s.

Fedex it be. Gsm your system appears to be in a crib (very live listening area) similar to mine, in that I too have very high (12’) ceilings and my speakers will be resting on the floor with an area rug inches away. I’m imagining the down firing woofer. Must be nice.

My room is 24 x 14.5 x 16 high. The Def 4s are on the long wall and within a couple of inches of the back wall. However, the room is one end of an open plan that is about 45' long, albeit broken up by fireplace, kitchen, mezzanine study above the kitchen, etc. There are no rugs on the floor. I was lucky in that Sean delivered them during one of his East Coast trips and dialed them. Bass is very deep, very tight. The SPL vs frequency curves on the Def 4 spec sheet are from my room.