IBM is not known for its support on OpenSource software. What is available is mostly ancient stuff. I'd suggest an upgrade: of the OS. AIX sucks, all other OS's do better: Linux, Solaris, and HP-UX are good options for AIX replacements, they all have recent perl builds available.

You have perl5.8.9 that probably conflicts with other perl versions hanging around.

Knowing the above reputation, is /opt/freeware providing you with a recent enough version of libxml2?