The MWE below demonstrates that I have a distinct lack of symmetry in the space between the horizontal lines and chapter title text despite employing the solution in Consistent Line Spacing in Customized Titles .
The meaningful difference between this MWE and those provided in the linked question/answer is the inclusion of setspace and parskip. I originally worked around this by using two different point sizes, but this limited my minimum separation distance and it's not the most elegant solution, so I would like to fix this properly, even if that means I shouldn't be using these packages (but if this is the case I would like some help figuring out why that is the case so I can try and figure out if I can fix the incompatibility with a renew command or if I have to remove all commands provided by these two packages in all my documents sharing this cls file).
\documentclass{report}
\usepackage{setspace}
\usepackage{parskip}
% CONFIGURE PAGE AND PERIOD SPACING
\onehalfspacing
%\doublespacing
%\singlespacing
\frenchspacing
% CONFIGURE HYPHEN RESTRICTION CRITERION
\righthyphenmin=6
\lefthyphenmin=6
\usepackage[small,md,explicit]{titlesec}
\makeatletter
%http://zoonek.free.fr/LaTeX/LaTeX_samples_chapter/0.html
\def\thickhrulefill{\leavevmode \leaders \hrule height 1ex \hfill \kern \z@}%
\def\@makechapterhead#1{%
{ \begin{singlespacing}%
\parindent \z@ \centering \reset@font%
\thickhrulefill\quad%
\large \bfseries \@chapapp{} \thechapter%
\quad \thickhrulefill%
\par\nobreak%
\vspace*{6\p@}%
\interlinepenalty\@M%
\hrule%
\vspace*{2\p@}%
\Large \bfseries \strut#1\strut\par\nobreak%
\par\nobreak%
\vspace*{2\p@}%
\hrule%
\vskip 20\p@%
\end{singlespacing}%
}}%
\def\@makeschapterhead#1{%
{ \begin{singlespacing}%
\parindent \z@ \centering \reset@font%
\thickhrulefill%
\par\nobreak%
\vspace*{6\p@}%
\interlinepenalty\@M%
\hrule%
\vspace*{2\p@}%
\Large \bfseries \strut#1\strut \par\nobreak%
\par\nobreak%
\vspace*{2\p@}%
\hrule%
\vskip 20\p@%
\end{singlespacing}%
}}%
\makeatother
\begin{document}
\chapter{Text Here for Chapter Title}
\end{document}
Update: Re. Asymmetry
Swapping out the following for chapter titles should reproduce inconsistent spacing. I will use short titles so the symmetry isn't complicated by the interline spacing of the lines of the title. Strut seems pretty necessary here to ensure these lines are consistent, but it looks funny to me when this same logic is applied to hanging characters on the last line before the drawn horizontal line. I will demonstrate.


\newlength\oldparskip \setlength{\oldparskip}{\parskip}before loadingparskippackage and then use\parskip\oldparskipjust before\parindent \z@– touhami Oct 12 '15 at 06:16