Marr

As far as I know the infused xp on armor comes from the Ars Magica 2 mod. Basically you kill mobs, armor gains some xp, and eventually you can use an "Armor Imbuement Table" to add special properties. The Arcane Compendium (book you make to start using the mod) goes into greater detail upon creation of the table. I'm not sure if this is right but I believe the random music note is from the Zelda mod, and it means you are close to a hidden room/block.

I've gotten the same exact crash log as you Targren. Do you remember what you were doing when it first crashed? I've been able to reproduce the exact same log every time by traveling too fast through chunks, usually by means of flying.