My suggestion is to make it possible to listen to them online. No long downloads anymore. Stream them. And have a voting feature right beside the streamable music, so voting can be done right away and very comfortably.
I like the music of Jean-Michel Jarre, and of Vangelis. Music for Space Engine should be inspired by them. I am going to listen now to the songs and vote...
Added (29.10.2014, 05:14)
Okay, I voted. I listened to the soundtracks not as dance music or regular songs to listen to, but under the condition of soundtracks that will repeat often, play endlessly, and have to make a descent background for spending hours in the game.
Soundtracks with loud hip hop rhythms I gave a lower rating, soundtracks with not much contrast I gave a higher rating as they have to line up with each other for many hours.
There were only two soundtracks I gave the full 5 points. One of them had some sound effects in it that could be interpreted as alien life forms, but in a descent way. That soundtrack inspired me, and fits greatly to what Space Engine is about: alien worlds, with or without life.
Having listened to all soundtracks, I strongly would want to encourage all sound artists, to use more alienized FXs in their musics, and to abandon dance rhythms. Concentrate on long-lasting, spherical sounds. Add strange-sounding FXs, like modified whale singing, but only a few of them, not too often. Add also short sequences of strange sub rhythms, fading in and out, like you pass by an alien world and can hear the pulse of their alien civilization. Add starnge-sounding speech segments of aliens. And also a very few natural sounds, like storm, wind, fire, rain, drops, waves, and such. This all is what is in our minds when we imagine other worlds. Coming close to a star, let the music transfer or get an underlaying of some hot percussion of Geiger counter clicks (measuring radioactivity), or so. Also, listen to the start music of the German version of the 1980s cartoon series "Captain Future" - their title song could inspire a possible start-up theme for Space Engine, except the beat rhythm sequence somewhere in the middle of the Captain Future theme soundtrack.