Yeah cheers. Figured it out however certain tracks seem to just crash just game such as changing the menu theme, can't seem to pinpoint the cause of the crashes. Had other tracks work fine.
Yeah, I had trouble with the menu theme. I somehow got it working after some work, but I have no idea what I did differently to make it work, lol. In fact, I'm pretty sure I just did something I had already tried before and then it suddenly worked. If I figure out what I did differently, I'll let you know.
EDIT: Okay, I see what happened now. I did try something I had before and now I realise why it's working this time. I don't know if it's doing this for you, but for me I have to repack the music files twice before they are heard in game. If I repack just once I get no music whatsoever.
Anyway, regarding your crashing (I apologise if you've already done these - just offering potential solutions!). One reason could be because of the akb header you are copying. You need to copy the entire header (everything before the first "OggS" in the hex code). In the menu theme, music033, that's everything up to offset 00000130.
I notice you said "certain tracks", so it's not just happening to you on the menu? The only other reason it would crash (besides not copying the full header code), that I'm aware of, is the file size. This is something I discovered while audio modding Final Fantasy IV - if you replace an audio track with one which has a smaller file size, the game will crash when it tries to play it. For example, the meeting theme (music018) is 1372kb. If you replace this with something smaller (even by 1kb) the game WILL crash when it tries to play it back. Therefore, all audio tracks you put into the game must be either the exact same size or larger than the original so they will play in game. I have still not figured out how to get around this, so I just work with it and make my files as close to the original as possible (making them slightly larger).
If you figure out a solution, let me know! Likewise, if I figure it out I'll post here.
The thing I'm trying to work out now is why the game butchers the audio quality. The tracks I'm putting in don't sound anything like what they do in-game, so there's something weird going on. It's likely an issue with the audio engine itself, meaning it's very unlikely we can fix it.