The group, interestingly enough, is named for the number of members: two, Shiina Nagano and Minami Takayama(real name Arai Izumi). Nagano doesn't actually sing or speak, although he is semi-talented at running a synthesizer. On the other hand, Takayama has appeared as a seiyuu (voice actor) in a number of popular anime titles, such as Magic Knights Rayearth(as Ascot), Ranma 1/2(Tendou Nabiki), Kiki's Delivery Service(Kiki and Ursula), and Record of Lodoss War(Seeris).
In the beginning, the group produced sappy, emotional songs, while still maintaining a hardcore dance beat. The Gundam W songs, as well as other excellent tracks such as Endless Love, Silent Cruising, and Trust Me exemplify this. However, in my opinion, the group has not really progressed. Instead they have fallen into the "Crazy-techno mindless dance dance revolution" trap that so many other artists have fallen victim to. Simply put, their most recent music lacks the emotion that set Two-Mix apart from other J-Pop groups. Still, if you're into the crack-like substance that is J-Pop and techno, Two-Mix's early albums(Two-Mix:BPM 132, Two-Mix:BPM 143, Two-Mix:BPM 150 MAX) will help feed your addiction.