I would like to change chapter layout/heading to contain more information. I found this question where a subtitle is added that contains information about original authors. However, I would like to include speaker (basically similar to author), event (optional) and date for each chapter so that it would look like this:

I also found another question that achieves additional information in the ToC but I would like to automate the entries by already specifying the text when defining the chapter.

I am a latex beginner and do not really understand the code. However, I tried to modify the above mentioned code to add not only one field with additional information but three. This unfortunately works only partly as I would have expected. Below follows my working example:

\documentclass{scrbook}

\usepackage{titletoc}
{\titlerule*[0.3pc]{.}\contentspage}

\usepackage{xparse}
\NewDocumentCommand \talk { m m o m }{
\IfNoValueTF{#3}
{\chapter[#1\\\textit{#2, #4}]{#1\beneathtitle{#2}[]{#4}}}
{\chapter[#1\\\textit{#2, #3, #4}]{#1\beneathtitle{#2}[#3]{#4}}}
}

\NewDocumentCommand \beneathtitle { m O{} m }{ \\
\parbox{\textwidth}{\Large\textit{#1}

\Large#2

\Large#3}
}

\begin{document}

\tableofcontents

\talk{The puzzling evolution of giant DNA viruses}{Matthias Fischer}[SFB Seminar Series]{21.10.1988}

In the viral world, size is usually defined by genome and particle size  […]

\end{document}