Since there's no other downloadable soundtrack of this sweet game around, I made one myself using the youtube videos of the soundtrack. Being a recording of a recording, don't expect top quality sound.
Volume was adjusted and some tagging was done.
http://www.mediafire.com/file/uklir887w2uvv84/Helldivers_OST_%28YouTube_recording%29.rar

Thanks for the effort. You don't really need to record Youtube audio, though. There are many ways to just rip (demux) the audio stream so you don't lose any quality, which is usually pretty low to begin with. JDownloader and Video DownloadHelper are but two examples. But thanks again!

I did use a site that converted videos to mp3s directly, which went rather fast so it probably did something like that. Didn't know it kept the quality intact though, good to hear!