 "Two children’s operas" were premiered by the Athens Opera (1998) and the Messinian Theatre (1999) to critical acclaim and commercial success.Xanthoulis has been invited by four American universities and the Music University of Tien Jin, China, in 2000 and 2001 for recitals and lectures on Greek music from the Antiquity till nowadays.His investigation and translations on the theory of the ancient Greek music was presented in lecture at the Boston University in 2003 at the Concordia University (Montreal), and in Ottawa.