[jpstewart]

2. FreeBSD ports man2html - appears to also include a cgi plugin: man.cgi which again does not work with IRIX pages

FWIW, man2html cannot work with the man pages as shipped with IRIX.  SGI shipped pre-formatted man pages ("catman" format) that could be displayed as-is.  But man2html is designed to take the nroff or troff source files and format them as HTML.  Most Unix variants shipped those source files, to be formatted to fit your terminal at run-time.  (Sometimes pre-formatted ones would be cached for subsequent display, but storing the catman files was optional.)  SGI never shipped the source files for their man pages.  On IRIX, you needed the add-on Documenter's Workbench to get any of the roff formatters and associated tools, so there was no point in them shipping the unformatted man source since few people would have been able to use it.

And that's why it will always take some extra effort to display IRIX man pages on the web.  They're distributed differently than usual.