Hi and welcome to rockbox development! Your best chance of understanding how rockbox works is to read the code and ask specific questions in irc, this list will probably get you an answer too but not as fast :)
There is no single way to voice something, check out how it's done in other places and the relevant worker functions in talk.c. The "open with" dialog is actually just the file browser showing the viewers dir so maybe it will "just work" if you put .talk clips for the viewer files in there. Nils
