Long story short, I downloaded the .vol reader application and MFaudio hoping that I would be able to find it. Unfortunately, it only gave me the race start song and finish from GT2. Daiki Kasho's "Mirage" was also in there but not the actual menu song. I'm asking here because it hasn't been uploaded online and I haven't really been able to get a response from people that I've asked. For anyone wondering, it's the early/in-game version of "An Endless Journey" that was only used in that specific demo. EDIT: Here is a video with the in-game music just for reference.