You could just find the sound folder in your Sins of a Solar Empire folder and copy them from there (the sound effects are in there too but it the name should tell you which one is which). They are in Vorbis Ogg format, but most media players should be able to play them and there are many free converters that can convert them into MP3.

Windows media player can play them too, but you just need to download some vorbis directshow thing for it.

You can find it on google

Yes you can. You can go to the mod folder, And make a Folder with a mod name of your choice eg."Music mod"

And in that folder you make another folder called "Sound" .

(The mod folder is MyDocuments/Appdata/Local/Ironclad Games/Sins of a solar empire/Mod-Entrenchment v1.401)

Now you just put bunch of Music you like in .ogg folder and name each one the same as the original sins music names Such as

Battle 1

Vasari Theme    .....etc

When you go into the game, all you gotta do is enable this little mod you made, And its 0 checksum so you can play with it online too.

I play with my custom musics all the time.

I just turn the music off and run iTunes in the background. I've taken to doing that in pretty much all of my games at this point because, like CitizenGeneral said, after 100's of games it starts to get repetitive

Nope, I leave those on. I don't mind them as much for some reason.