Imho you don't need multibib because biblatex already includes this functionaility. This answer explains parts of it.
Im suspecting that you would like different sections for references, Software and books. \printbibliography excepts optional arguments, please also refer to section 3.7.2 The Bibliography of the biblatex manual
So for your use case I would expect it to be like in this answer
\documentclass{scrbook}
\usepackage[backend=bibtex]{biblatex}
\defbibheading{ref}{Primary Works Cited}
\defbibheading{software}{Software Cited}
\defbibheading{books}{Books Cited}
\addbibresource[label=ref]{references}
\addbibresource[label=software]{referencesSoftwares}
\addbibresource[label=books]{referencesBooks}
\begin{document}
\begin{refsection}[ref]
\nocite{*}
\printbibliography[heading=ref]
\end{refsection}
\begin{refsection}[software]
\nocite{*}
\printbibliography[heading=software]
\end{refsection}
\begin{refsection}[books]
\nocite{*}
\printbibliography[heading=books]
\end{refsection}
\end{document}