in general, for params and variables its better not to do this:
<xsl:with-param name="troff">\\\(\?s</xsl:with-param>
and instead do this:
<xsl:with-param name="troff" select="'\\\(\?s'"/>
so it gets set to a string rather than a temporary tree with a document
node, a text node child, which is more expensive to build.

It depends a bit what the ascii transliteration looks like but it looks
like it would be worth merging some of the replacements to save
repeatedly re-searching for \\\(
something like
<xsl:analyze-string select="." regex="\\\\\\(\\\?([a-z])"
  <xsl:matching-string>
    <xsl:choose>
      <xsl:when test="regex-group(1)='s'">...
      <xsl:when test="regex-group(1)='c'">...


David