As far as I know, and I'm a huge fan too, there is no version what-so-ever that works with 1.2.5. You'll need to rollback to 1.0.0 to play the Aether. I think there was a fan update to 1.1 but I don't know where it went.
I have MC 1.0.0 and started playing a few days ago. I sure hope this is not a lost mod. This is a very great mod. Allot of work and care went into it. A shame if it's dead. All the required parts needed for this mod is still downloadable. The normal thread was locked because ppl were spamming for update. I think the creator is waiting for mod API to come out.