I used to own a pair of regular Mani-2 for about a year. I got me a new set of Signature Mani-2 about two months ago.
First the main difference is closer tolerances of the drivers, and better internal wiring. Soundwise, you must have pretty good source, preamp, amps & wiring for the signatures to show their edge over the regular ones. Not to mention quality recordings and hearing. The tweeter is a Seas unit and the midbass are Dynaudio, both companies are very good and manufacture drivers that are second to none to begin with. The Signatures also have top line WBT bindding post, very few amps under 15K have them. There is an edge, but please be advised that is very subtle. To be quite honest with you with 95% of the music that I listen to there is basicaly no difference at all. I listen mostly to rock(english and spanish) and brazilian music. On the other hand my some audiphile recordings, mostly clasical music there is a subtle improvement in the sound, mostly in the top end. I did change mines because I got the first pair without even hearing or looking at them, didn't like the mahogany finish. I sold them and got Signatures in chery, at that time the difference was just under $500.00 . If I were to pay $700.00 more for the Signatures I would be more than happy to buy the regular ones and allocate those $700.00 to upgrade the weakest link in my gear. With either one you choose you will be very happy, regardless of price, these have to be the best speakers I have ever owned and I have gone into the 15K to 20K range.
Hope this helps, Hector.