There are at least 8 artists with the name Amadeus.
1: A Japanese rock band formed in 1996
2: A Finnish tango/schlager singer who took part in the Finnish national final of the 2010 ESC
3: A DnB DJ
4: A band from Romania
5: A pop/rock band from Serbia
6: A Metal band from Belgium
7: A Finnish pop/rock band
8: A rock band from Hudson, Ohio that has since broken up
9: An English electropop musician
AMADEUS, the band, was a Japanese rock band formed in 1996 by ex.AFTER IMAGE members Seiji (vocal), Miyu (bass) and Hiron (keyboards). A new addition to the band was Nene: the female soprano vocalist. The band's music contained a lot of influences from composers such as Beethoven and Mozart, mostly noticeable in Hiron's keyboards, and they didn't have a drummer so they utilized a drumbox. Only 1 song by them features guitar, "虚像の神" , which was played by guest guitarist SINYA (ex-GELLONIMO, SPEED SLAVES). Most of their songs were more focused on Hiron's impressive keyboard skills as well as the Seiji / Nene vocal duo.
However; Nene and Seiji left the band, leaving Hiron and Miyu as the only remaining members. Nene appeared in Art Marju Duchain before they broke up but never got to release anything with them. Seiji later found himself in Brain Hacker and helped out with Hizaki's solo work (vocals on "Mizerable").
Seiji is currently Moi dix Mois's vocalist under the stage name "Seth."
Brain Hacker is now disbanded and has reformed under the name Art Cube, and Seiji changed his name to Z (Zeta) while still being a part of Moi Dix Mois.
AMADEUS official HP
Amadeus is a Serbian rock band consisting of five members: Aleksandar Stanimirović (keyboards), Bojan Stanimirović (keyboards), Bojan Tašić (vocals), Bojan Zlatanović (drums, vocals), Milan Kordulup (guitar).
They started playing in 2002 and have released four albums so far: Kupi me (2002), Takvi kao mi (2003), 100% (2005) and Best of Amadeus LIVE (2007).
Amadeus Band official website
source: official website