The only part of the tweeter that was handed down from the old discontinued Sig line was the Gold Dome, not the entire tweeter... The Signature is a far more heavily designed tweeter, as well as the other items listed....
I have heard both the Energy 2.4i, and the Studio's when I was on the market, and I loved the Energy sound, but my room is huge and I felt I was getting more for my money with the Studio's... As I thought the bigger speaker was more important, and I really liked the looks of the Studio's better as well... great asthetics...
Both are great speakers, and you won't be disappointed with either..
Now I have had the Studio's for over a year, and they Rock Hard !!! But they are bright... I have to EQ that brightness out, although my room is very bright as well, and I feel that has alot to do with it...
I just recently bought the new SVS - MTS system, and I have to say, they are fantastic... not as bright to me, just a smoother sound, but not lacking in detail in the tweeter, which is extremely important to me, where soft dome tweeters usually sound muddy or muffled in that department... Unfortunately the new LTS line won't be out until late '08 or early '09, I am very interested in what they come up with...