Another thing I would like to say: we know that the speech/voice files are the RWS files in the SPEECH folder. And it turns out that the Sekens are related to those files. In fact they have the same IDs and same order.
So basically, 1 Sekens => 1 RWS file containing all voices.
Another thing I realize is that, it seems that the devs actually have every voice audio associated to each text line. In fact, if we look at the Remasters, we have confirm it there are voice sound files, each with an ID that matches a text ID: