I have been playing with my old Sega Megadrive a bit as well, so I ended up making a small detour and looking at the Wing Commander Sega CD files. Long story short, things went better than expected, so was able to quickly make an extractor for Sega CD speech! You can find my little SegaRIP utility here. Open your cmd window and type something like: segarip RIG.DAT
Please keep in mind that there may be a few voices in the game that are not extracted properly. I'm still looking into that. However, I decided to release a first version of this extractor since it does seem to work well for the large majority of speech in the game, so it could still be useful as is.
Cool stuff! This little adventure made me appreciate the Sega CD port of WC1 a bit more.