We're interested in shipping it to the U.S.
I shipped some large packages from the U.S. to Poland with them, and it worked flawlessly. Perhaps they ship from Poland to the U.S. too, and you can rent a whole container? This is an option I have been considering for some time, because I too have an upright piano that I want to ship from Poland to the US. This is a 'Legnica', and I am willing to pay for renting a container because of the sentimental value of the instrument. Besides, it is also very well made (compared to these $4,000 mass produced Yamahas). If you rent the whole container, you can package the instrument well and be reasonably certain that it is going to arrive in good shape.
Or maybe you would like to share a container? This may be hard to arrange, but we can ask Polamer.