Quick update for you: I'm still here and working on it. I had some issues with the SegaCD and HCI's extraction tool. For one reason or another the debriefing audio for Gateway Mission 2 just isn't in the debriefing file. It plays in the game but couldn't find any reference in the Deb.dat file.
Also missing some other dialog like inflight comms and story narration. The files are there but just don't extract using the tool. So after some deep digging I ended up finding a program called SnacherPCM2Wav which basically converts binary files to WAV. It sucks a little because it also converts the code in between to broken audio and static, so I need to do edit them and separate the missing files manually. Though I have successfully found and extracted the story narration files that I was previously missing and looking for the others.
So basically converting all the SegaCD version code to WAV and scrubbing through them looking for missing lines. So lots of work but progress is being made. I've also had to work a little this last week and some family things going on but never fear I'm still on the case. :D Cheers