Square Enix is including bonus content with Final Fantasy XIII-2's various CDs. The game's single CD, from Avex, includes Diva's Mic and Diva's Headphones. The game's mini album CD, also from Avex, includes Goddess's Bangles and Goddesses's Earrings.
So which CD should you get for the ultimate accessory set? It turns out that if you do want the ultimate accessory set, you're going to have to get both CDs. If you have all four accessories equipped, you'll gain a four accessory chain ability: increased CP
The items also have individual and combined effects outside of the grouping of all four. On their own, the Diva Mic and Diva Headphone items respectively up your item drop rate and gil earning. Together, they combine for a two accessory chain ability: rare item drop rate up. The Bangle and Earring items respectively make your character stronger and gain added magic strength. Together, they combine for a two accessory chain ability: strengthened item recovery.