Sortierung nur nach Erstautor dann nach Jahr, dann Zweitautor?

\documentclass{article}
\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}
\usepackage[babel, german=quotes]{csquotes}
\usepackage[backend=biber,citestyle=numeric,bibstyle=authoryear,firstinits=true,terseinits=true,maxbibnames=99,sorting=sortname]{biblatex}

\DeclareStyleSourcemap{
    \maps[datatype=bibtex]{
      \map{
        \step[fieldsource=author, match=\regexp{(.+?)\sand}, final]
        \step[fieldset=sortname, fieldvalue=$1, final]%$
      }
      \map[overwrite]{
        \step[fieldset=sortname,fieldvalue={\space and },append]
        \step[fieldset=sortname,fieldsource=year,origfieldval,append,final]
      }
      \map[overwrite]{
        \step[fieldsource=author, match=\regexp{(\sand\s.+)}, final]
        \step[fieldset=sortname, fieldvalue={$1}, append, final]%$
      }
}}

\DeclareSortingScheme{sortname}{%
  \sort[final]{\field{sortname}}
  \sort{\field{title}}
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\RequirePackage{filecontents}
\begin{filecontents}{bib.bib}

@article{ref1,
    author={J. Kjaergaard},
    year={2012},
    title={abc}
}
@article{ref2,
    author={J. Kjaergaard and C. L. Petersen and A. Kjaer and B. K. Schaadt and J. K. Oh and C. Hassager},
    year={2006},
    title={def}
}
@article{ref3,
    author={J. Kjaergaard and E. M. Snyder and C. Hassager and J. K. Oh and B. D. Johnson},
    year={2006},
    title={ghi}
}
@article{ref4,
    author={J. Kjaergaard and P. Sogaard and C. Hassager},
    year={2006},
    title={jkl}
}
@article{ref5,
    author={J. Kjaergaard and J. Hastrup Svendsen and P. Sogaard and X. Chen and H. Bay Nielsen and L. Kober and A. Kjaer and C. Hassager},
    year={2007},
    title={mno}
}
@article{ref6,
    author={J. Kjaergaard and E. M. Snyder and C. Hassager and T. P. Olson and J. K. Oh and B. D. Johnson and R. P. Frantz},
    year={2007},
    title={qrs}
}
@article{ref7,
    author={J. Kjaergaard and D. Akkan and K. K. Iversen and L. Kober and C. Torp-Pedersen and C. Hassager},
    year={2007},
    title={tuv}
}
@article{ref8,
    author={J. Kjaergaard and J. Korinek and M. Belohlavek and J. K. Oh and P. Sogaard and C. Hassager},
    year={2006},
    title={wxy}
}    
\end{filecontents}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\addbibresource{bib.bib}

\begin{document}
\section{test}
\cite{ref1} and \cite{ref2} and \cite{ref3} and \cite{ref4} and \cite{ref5} and \cite{ref6} and
\cite{ref7} and \cite{ref8}.
\printbibliography
\end{document}