Ok the original music is great really fantastic but… after many many of hours it unfortunately gets boring… too repetitive for me. So i if someone of you want to change music you will find here info how to do it and some members custom music. Hey and if someone of you already changed the in game music PLEASE SHARE IT WITH US 
So the solution is custom music…
How to do it: it is simple you just replace the original files in (…\Gratuitous Space Battles\data\sounds\music) folder with your files. And by replacing i mean coping your music file(it can be ogg or mp3 i didn’t tried other) into that folder and renaming it for example you want to change alliance_battle tune you must rename your file to alliance_battle.ogg (!! Remember that if you have mp3 file you have to rename the extension also)
For protection i keep the Original tunes in Original folder…
And here are my files:
alliance_battle.ogg
empire_battle.ogg
federation_battle.ogg
i didn’t knew that there are links limit
and here are the rest of links
main_title.ogg
rebellion_battle.ogg
setting_up_ships.ogg
all of them are currently from Unreal Tournament. i am planing to find more but it requires time.
So please help save time for searches post your custom music NOW 
there should be a way to add more music 
then if that exist …'type “epic music” into youtube search and put most of those in a mod ? XD
Yes i look for more gratuitous reply
The first time I tried substituting a GSB music file for one outside the game, GSB crashed on restart with an error message. Evidently the music does need to be in Ogg Vorbis format. Any music in MP3 format did not work for me, especially if all I did was change the file extension in the filename. It also crashed if I used an “actual” MP3 file. No quick fix there.
The “full” fix wasn’t a big deal, though. I simply downloaded a free copy of Audacity: a very nice open-source audio editor. I made sure to move the Quality slider to “maximum” in the app’s preferences. Then I imported an MP3 of my choosing, converted it to .OGG, and saved accordingly. The resulting file was accepted by GSB and played without problems. At least, no problems from the game’s point of view…
I wish that I had an uncompressed, lossless file to use as my source, though. A .wav or an .aiff file would have been ideal for me. You might want to rip an uncompressed file directly from a CD source.
I heard a noticeable loss in audio quality with the first file I ended up with - fairly muddy and indistinct sound. That was because I had left Audacity’s preferences alone… I think the default save value for Ogg Vorbis format is level 8. I had to move it up to level 10 (the max value) and re-save. I’m not fully happy with having so much music of interest for GSB purposes but only having copies in MP3. Going from one compressed format and then compressing it a second time is not ideal, even if the source MP3 has a high bit-rate. I used a 256kbps MP3 as my source, and even with my less-than-ideal ears I could detect a slight loss of quality when playing that music in GSB. I heard a small reduction in treble/brightness, and the bass was better than before but still a little “mushy”. True, It wasn’t a big disaster, but I really was surprised that I could hear the difference. I really didn’t think that I would – my hearing is definitely not the best. This may have been because I was using a Classical composition for full orchestra, which is going to have a lot to lose when compared to standard rock band stuff.
As they say, “your mileage may vary.” Just be sure to use the best quality source that you can find before converting to .OGG!
just check with random file and it worked fine with me…(i have 1,38 version without expansions)
i renamed basshunter - tetris.mp3 into main_theme.ogg and it worked fine
I feel duty bound to point out that GSB’s sound engine should (it does on my system) play quite nicely with media players. You can happily turn off the music and have windows media player go through its playlist at the same time as running the game, if you so desire.
Heh, cliff, that’s my solution to not liking a game’s soundtrack: grab my iPod and play something on it.
Given what I’ve been listening to lately, that is, ironically, frequently another game’s soundtrack.
But in game music is nicely tunned with all the effects(the volume is just right to hear all the bangs and booms) not all tracks have normalized volume and alt+tab make sometimes game crash 
So I don’t know why you are so afraid to use my method…