If you want audio switch your language setting to Japanese. It’s that or the sound of silence.
Sega created the Challenge of Edy pack half a year after Valkyria Chronicles launched in North America. The time lag may prevented Sega from getting the cast to reprise their roles. That’s a possible explanation, not an official one. Whatever the case is, it might have been nice to hear about this before the content went live for people who prefer the English dub.