ItachiIshtar

And here's the Larxene silhouette battle with Shanelle Gray's battle grunts. Like the Zexion one, this is from a European release of 2.5, which still uses the English voice acting:

Just want to clarify something. The person who's doing that particular Let's Play is doing so using the English data on the Japanese disc via a hack. The English data on the Japanese disc is incomplete. I actually found the Zexion Absent Silhouette battle from a new European Let's Play, and it's definitely Vincent Corazza doing Zexion here: Compared to the Japanese Zexion battle voice: In short, it looks like we have the proper English battle voices for the Absent Silhouettes after all.