最近はTexinfoもDocBook形式に変換できるのね。
http://www.sra.co.jp/wingnut/standards/standards-ja_6.html
$ makeinfo --help
(略)
Output format selection (default is to produce Info):
--docbook output DocBook XML rather than Info.
(略)
makeinfo --docbook foo.texi write DocBook XML to @setfilename
(略)