He saw limited playing time in two seasons with the Cavaliers as the backup to All-Star center Žydrūnas Ilgauskas. After playing in just 43 games for the Cavaliers, Stack signed a contract to play in Europe and played for Gijón team from Spain's ACB for the 2000-2001 season.
The next season Stack moved to Israel and was signed by the Maccabi Ramat Gan team.
After the year in Israel he moved to Greece and was signed by Aris Thessaloniki and played there from 2002 to 2006, in all of those years with the team he won 1 EuroCup in 2003 and reached to the ULEB Cup final in 2006. He was then the highes paid centre in Europe.
While playing for Aris Thessaloniki, he adopted a Macedonian citizenship, so he can play as a European, out of the two non-Europeans per team policy in the Euroleague and Europe. He played for the Republic of Macedonia in several European and world championship qualifications, and he plays for that national team even today.