The second disc of that set contains more soundtrack music that didn't make the first release. The third disc is just Vangelis's modern noodlings inspired by themes from the soundtrack -- not very interesting and I am just short of being a hardcore Vangelis fan.
I'll put some things from the second disc on divshare. Back in 20 or so...
I picked those at random. The first CD of the 25 annv set is a remaster of the first release, and it's worth getting just for that. I had to listen to a few parts repeatedly because at first I thought they had also been remixed, but now I am convinced that the remastering was just that superb.
I may have been too harsh on the third CD because the first song puts me off. I am going to listen to it again but skip the first song. These three are random too.