There are a few things Japanese people (and me) do like, one of them is known as character song but I guess you already guessed.
What I was trying to say is that on August the 25th they're going to release two character songs CDs for Kuroshitsuji.
What you'll be able to find on these CDs are two songs for Sebastian's seiyuu Ono Daisuke and two songs but Finnian's seiyuu Kaji Yuuki
The official website has been updated with a preview for these four songs, so if you want to listen you just have to click Here