I looked into this a while back myself. At that time, Clavia was still using the same proprietary compressed format for some of their keyboards that the ddrum4 used. Because of that, they would not release the specs for the file format or the compression algorithm(s) they used.
That being said though, since the guys at 2Box have the history with Clavia that they do, they might be able to get permission to convert the sounds over to a compatible 2Box format, or possibly even gain access to the original recording samples to rebuild the sounds.
Either way, it'd be a lot of work and it sounds like Bengt and crew already have their hands plenty full making sure the product lives up to what they want it to be.