& statt , zwischen mehreren Autoren beim biblatex-Stil apa

% arara: pdflatex
% arara: biber
% arara: pdflatex
% arara: pdflatex
\begin{filecontents*}{\jobname.bib}
@article{Test.1,
  author = {Duck, Dagobert and Fritz, Peter and Nachname, Vorname and NachnameA, VornameA},
  title = {Testbeispiel},
  pages = {175--190},
  year = {2009}
}
@article{Test.2,
  author = {Mustermann, Max and Mustermann, Max},
  year = {1999},
  title = {Minimalbeispiel},
  pages = {512--530},
  volume = {21},
  journal = {Rundfunk und Fernsehen}
}
\end{filecontents*}
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[babel=true,german=quotes]{csquotes} 
\usepackage[style=apa,backend=biber,language=ngerman,apamaxprtauth=99]{biblatex}
\renewcommand{\finalnamedelim}{\addspace\&\space}
\AtBeginBibliography{%
  \renewcommand{\finalnamedelim}{\addspace\&\space}}

% === textcite ===
\DeclareCiteCommand{\textcite}
  {\renewcommand{\finalnamedelim}{\addspace\bibstring{and}\space}%
   \usebibmacro{cite:init}%
   \usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{textcite}}
  {}
  {\usebibmacro{textcite:postnote}%
   \usebibmacro{cite:post}}

% === parencite ===
\DeclareCiteCommand{\parencite}[\mkbibparens]
  {\renewcommand{\finalnamedelim}{\addspace\&\space}%
   \usebibmacro{cite:init}%
   \usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{cite}}
  {}
  {\usebibmacro{postnote}%
   \usebibmacro{cite:post}}

\DeclareCiteCommand*{\parencite}[\mkbibparens]
  {\renewcommand{\finalnamedelim}{\addspace\&\space}%
   \usebibmacro{cite:init}%
   \usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{citeyear}}
  {}
  {\usebibmacro{postnote}%
   \usebibmacro{cite:post}}

% === citeauthor ===
\DeclareCiteCommand{\citeauthor}
  {\renewcommand{\finalnamedelim}{\addspace\bibstring{and}\space}%
   \usebibmacro{cite:init}%
   \usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{cite:author}}
  {}
  {\usebibmacro{postnote}%
   \usebibmacro{cite:post}}

% === cite ===
\DeclareCiteCommand{\cite}
  {\renewcommand{\finalnamedelim}{\addspace\bibstring{and}\space}%
   \usebibmacro{cite:init}%
   \usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{cite}}
  {}
  {\usebibmacro{postnote}%
   \usebibmacro{cite:post}}

\DeclareCiteCommand*{\cite}
  {\renewcommand{\finalnamedelim}{\addspace\bibstring{and}\space}%
   \usebibmacro{cite:init}%
   \usebibmacro{prenote}}
  {\usebibmacro{citeindex}%
   \usebibmacro{citeyear}}
  {}
  {\usebibmacro{postnote}%
   \usebibmacro{cite:post}}

% ===

\DefineBibliographyStrings{ngerman}{%
  andothers ={et\addabbrvspace al\adddot},
  andmore ={et\addabbrvspace al\adddot},
}

\DeclareLanguageMapping{ngerman}{ngerman-apa}
\DeclareFieldFormat{apacase}{#1}
\addbibresource{\jobname.bib}
\begin{document}

parencite: \parencite{Test.1}

citeauthor: \citeauthor{Test.2}

\printbibliography 
\end{document}