This is an arranged album for Final Fantasy XI that was interestingly performed by 'The Star Onions'; a group comprised of several Square-Enix sound staff. From what I understand, on September 11, 2004, there was a special tribute night for the soon to be released Chains of Promathia expansion pack. The magazine Famitsu sponsored a Square-Enix organised concert in which 6 songs were performed from both prior OSTs; the original soundtrack as well as music from Rise of the Zilart expansion.
If you're like I am and have fun finding out more than you need to, why not try streaming this file in your media player? Disregard the Japanese, it basically says that the program is presented by Famitsu, and asks the audience to patiently wait for the concert to begin. Oh, and skip the first hour and a minute or so because that's when the actual concert starts. If you know some Japanese or just love the sound of it you can watch the rest, there's discussion on the expansion for you.
Given that 6 tracks were performed at the concert, it's a safe bet that they will be on the CD, but specific details have not yet been given.
Having never played FFXI, I can say this performance interested me. Not only for 'fresh blood' in Square-Enix's music talent, but especially because the composers themselves performed.