Strong Reverberating Voices?

Part of it is that he sings with good technique, meaning he uses his breath efficiently and opens his vocal pages enough to create a full sound. The other part is that the studio used reverb and probably an aural exciter effect to enhance his already-good technique. The reverberation you hear is basically harmonics inherant in good vocal technique. Opera singers don't use microphones, yet they can be heard over a full symphony orchestra; basically, the sound reverberates through the use of proper technique.