In my humble opinion the music played during Jupiter Jazz parts 1&2 is some of the most beautiful there is in the series. So just in case you were wondering what they were, here is a little information on the music featured in Gren's episodes! I highly recommend that you seek out the Cowboy Bebop soundtracks as all the music is pure gold!

Goodnight Julia
CD Found on: Cowgirl Ed OST
This is the heart breaking song we hear Gren playing when we first encounter him at Rester House, which we later find out he learned from the music box that Vicious gave to him.

Space Lion (orgel version)
CD Found on: CD Box Set Disk 2
Although Vicious tells Gren that the name of the song the music box plays is called "Julia," on the official soundtrack it's Space Lion (orgel version). Regardless of the title, it wrenches at the heartstrings just as much as the saxophone version.

Words That We Couldn't Say
CD Found on: Blue
This song is not quite as directly related to Gren, for it's the song that plays before he meets up with Vicious when Spike is flying around in the Swordfish.

Waste Land
CD Found on: CD Box Set Disk 2
The solemn trumpet piece that accompanies flashbacks of Gren and Vicious in the Titan war during their final rooftop confrontation.

Space Lion
CD Found on: Cowboy Bebop OST 1
The ending song for part 2, which is partially sax (Goodnight Julia), partially vocals in an unknown language, and entirely gorgeous.

Space Lion 4 Hero Remix
CD Found on: Music for Freelance
A remix of Space Lion by (you guessed it!) 4 Hero. It was never actually used in the series, and it doesn't really sound like the original at all..