I don't know anything about Kontact in particular, but to turn any
other VSTi track to audio, you Render the project. If you just want
that one track, you mute everything you don't need.
There's also a couple of other features that may be more what you're
looking for but I haven't used them yet, called "Stem Rendering" and
"Track Freezing". Check out sections 5.17 through 5.19 in the manual
for details.