The author mentions to be unsatisfied with the solution to use symlinks for finding DocBook XSL files. The correct way to reference DocBook XSL stylesheets is to use the HTTP URL to the stylesheet, which will be looked up in the XML catalog of your system. This catalog file maps URLs to files on disk and is managed by your package manager.
You should also forbid your tools to access these URLs directly (--nonet), as it would be incredicly slow and you rather want your build to fail in this case instead of downloading on-demand.
If you prefer to work with files instead of passing long URLs on command line, use a small wrapper file to import the real stylesheet and pass that on command line instead of using the URL. The advantage is that you can also put additional <xsl:param> tags to customize the output right into this file.
<?xml version='1.0' ?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:import href="http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl"/>
<!-- put additional xsl:param here -->
</xsl:stylesheet>
You should also forbid your tools to access these URLs directly (--nonet), as it would be incredicly slow and you rather want your build to fail in this case instead of downloading on-demand.
If you prefer to work with files instead of passing long URLs on command line, use a small wrapper file to import the real stylesheet and pass that on command line instead of using the URL. The advantage is that you can also put additional <xsl:param> tags to customize the output right into this file.