Adam, thanks for the link: very useful.
I have been able to map the APL+Win font to UTF8. Now I can translate []av to utf-8, write it to a file and have C# echo the file into the APL+Win editor (or Word etc) without any (fonts) problems. See the attached WMV.
What I wanted to do was to echo the file into a Visual APL session: there are problems here as the fonts are all garbled up; it would appear that the APLNEXT font is using some other mapping which I am trying to figure out.