Hi,
the XMP SDK does support read/write of the BEXT chunk in WAVE files since CS6, i.e. the current version of the SDK supports this functionality.
For more details on the mapping to XMP, please see the XMP specification part III, section 2.3.2.2.
There have been requests about iXML in the past, but so far not strong enough that it made it to the top of the priority list Image may be NSFW.
Clik here to view.
Regards
Jörg