Which XSLT processor and which version of XSLT can you use? With the commercial versions of Saxon 9 you can use XSLT 3.0 and
<xsl:template match="pre">
<ce:section-title>Pre</ce:section-title>
<xsl:apply-templates select="parse-xml(.)"/>
</xsl:template>
<xsl:template match="p">
<ce:para>
<xsl:apply-templates/>
</ce:para>
</xsl:template>
<!-- now add similar templates here for transformation of strong, em etc -->