Minimal example:
\documentclass{report}
\usepackage{amsmath}
\begin{document}
\begin{alignat*}{2}
A \hspace{12.5pt} & \hspace{12.5pt} && A \\[10pt]
B \\[10pt]
C \hspace{12.5pt} & \hspace{12.5pt} && C \\[10pt]
D \hspace{12.5pt} & \hspace{12.5pt} && D
\end{alignat*}
\begin{alignat*}{2}
A \hspace{12.5pt} & \hspace{12.5pt} && A \\
\end{alignat*}
\begin{equation*}
B
\end{equation*}
\begin{alignat*}{2}
C \hspace{12.5pt} & \hspace{12.5pt} && C \\[10pt]
D \hspace{12.5pt} & \hspace{12.5pt} && D
\end{alignat*}
\end{document}
I'd like the B to be centered with equal vertical space between the lines.
Edit.
My original question was not sufficiently precise. I do not want the horizontal spacing between the aligned columns to change. In practice the entries will be quite wide. Please see the new example.
\documentclass{report}
\usepackage{amsmath}
\begin{document}
\begin{alignat*}{2}
A \hspace{12.5pt} & \hspace{12.5pt} && A \\[10pt]
MMMMMMMMMMMMMM \\[10pt]
C \hspace{12.5pt} & \hspace{12.5pt} && C \\[10pt]
D \hspace{12.5pt} & \hspace{12.5pt} && D
\end{alignat*}
\begin{alignat*}{2}
A \hspace{12.5pt} & \hspace{12.5pt} && A \\
\end{alignat*}
\begin{equation*}
MMMMMMMMMMMMMM
\end{equation*}
\begin{alignat*}{2}
C \hspace{12.5pt} & \hspace{12.5pt} && C \\[10pt]
D \hspace{12.5pt} & \hspace{12.5pt} && D
\end{alignat*}
\end{document}
It should look like this:
A A
MMMMMMMMMMMMMM
C C
D D