If any program can work with both .nks and .nki files, it would be KONTAKT or similar software produced by Native Instruments. NKS is a protect archive format and normally it is not supported in 3rd party tools, so using the original programs seems to be the only choice.
Convert Native Instruments archive file to Native Instruments instruments sample.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert nks to nki on Windows
A dedicated audio sampler for Microsoft Windows, KONTAKT delivers a number of large-scale enhancements, extending the creative power of the industry standard sampler further than ever before.
Convert from nks file
to nki file
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.