Welcome to Android Central! Can you locate the voice recording files? If so, are they mp3, wav, or ogg files? Those are the kinds of files that can be used as notification tones. If you can locate the files and they are in one of those formats, then move or copy them (using your file manager) to the Notifications directory on Internal Storage.
As ManiacJoe mentioned, though, apps don't always let you customize notifications for individual contacts. It's possible for incoming calls, but not always for text messages (and I don't think it's possible for emails).