Joseph Pramberger did indeed work for Steinway for a while. I am not sure of his capacity there. Rumor is that he had a falling out with the Steinway folks and took his expertise to Korea, where he joined up with Young Chang to create the Pramberger series of grand pianos.
Last year, when Young Chang was undergoing its financial difficulties, it was going to be bought out by Samick. However, the Korean government forbade the sale (monopolies and all that) and forced Young Chang to re-organize. As part of the deal, the Pramberger name (and name only) was retained by Samick. The design is still owned by Young Chang. Offhand, I don't recall the name that Young Chang (now owned by Hyundai) is using for the Joseph Pramberger designed piano.
So, when one talks about Pramberger, one has to ask, "Which One?" There are two - the Young Chang Pramberger, and the Samick Pramberger. They are completely different pianos with the same name.