How about this idea. Take the head out of the amp and box that up separately, take the tubes out, label them for re installation , the tubes can be wraped in the smaller bubble wrap. Place the bubble wraped tubes strategically on the head, tape down with masking tape if necessary. Wrap the head in a couple of layers of heavy duty bubble wrap. Get a heavy duty box a little bigger than you think and put the head in the box with a bunch of those packing peanuts around it. All the while keeping the USPS size a and weight regulations in mind.
Now you can ship the head via USPS, priority mail, insured, delivery confirmation. This is way better than shipping UPS.
Carefully measure and weigh the cabinet with the speakers and if it can go USPS, you are pretty good to go.
Box it up and ship that via USPS if possible. This will be the cheapest way to go. If the cabinet does not make the USPS, then UPS can ship the cabinet. Trust me on this one, from personal experience, UPS is a nightmare to try and get them to actually pay a claim, and they destroy tons of stuff. Fed X handles high value items carefully.