Since I would very much like to be able to use portMIDI with Perl5 I would like to know how hard it would be to port the Perl6 portMIDI wrapper to Perl5.

Perl6 and Perl5 are very different systems, better try to use a native interface to the library, i.e. XS or perhaps a Module based on Inline::C (which does most of the nasty XS stuff behind your back).

Alexander