Whatever you want, although if you want specific suggestions, I have a few. Right now we're lacking some early society stage themes - tribal, antiquity, medieval, etc. These could be right down your street. My personal idea is that music going through stages should start with atmospheric synthesizers and slowly morph into orchestral, with rhythmic and percussive elements added as an organism begins to civilise, then return to synthesizers post-Industrial but with greater emphasis on rhythmic pulse. Of course, this is just a vague idea, and there are lots of variations on these depending on the player's situation.
OpenAL, I believe. Yeah, maybe not quite as glamorous.
Most likely not. We'll have a theme or two for each possible scenario in each stage, then move between them randomly depending on how that changes. For example, if a player in the Industrial stage is a Communist civilisation, they'll hear the Communist peace theme for a few minutes, then once it's over another one such as the generic Industrial theme will enter. If at any point they declare war, whatever theme is playing fades out and the Communist war or Industrial war theme plays.
Not sure at the moment. We've had discussions about dynamic music before (don't click any of the hyperlinked words in the posts, they're advertisements added by the forum supplier, one of the reasons we moved to a new one). If you mean recreating the motif with different instruments and styles for another place, then yeah we'll probably end up doing that, but it's not necessary.
We'll need relaxing, tense, tranquil, victorious and sad theme moods, and probably many more. Generally, if it's a peace or generic stage theme, it'll be relaxing and ambient, themes for mysterious environments should be tense and disturbed, and war or predator chase themes should be upbeat and strident.
I probably answered this in with the first one.