If you haven’t figured it out yet, the answer is, unfortunately, basically “no”. Newer versions of Kontakt can open up libraries made with older versions, but there is no way of opening up a new library with an older Kontakt.
It sort of has to be that way – if the new version of Kontakt has a new kind of filter or effect or something, it’s not possible
for the old version (which doesn’t have that filter or effect) to open the NKI properly. However, it’s a shame Kontakt doesn’t have an “save minimal compatibility version” or something that saves sample and group mapping and loop points and even envelopes in a fashion compatible with say Kontakt 2, that almost everyone could open, and that’s the most tedious part of recreating the NKI by hand in an older version. I guess NI would rather have us shell out for the new Kontakt!
Thanks for your comments. As you know, Pianobook is not just a resource, it is a community. As such, you can help us by picking an instrument you particularly like in Kontakt, and translate it into a free format such as DecentSampler or SFZ. Then upload it back to the community.
If everyone did just one translation, we would quickly have free open versions of all the instruments (we need about 300 done).