Dix was a highly successful amateur athlete, setting a state record in the 100 m and trying out for the US Olympic Team at the age of eighteen. He joined Florida State University and in his first year he broke the 100 m American junior record and won at the NCAA Outdoor Championships. After a fourth-place finish at the 2005 US Championships, Dix continued with his collegiate success, setting an NCAA record of 19.69 seconds in the 200 m and coming within one hundredth of the 100 m record. He completed a 100 m, 200 m, and 4×100 meter relay sweep at the 2007 NCAA Outdoor Championships, the first to do so since John Carlos in 1969. He closed his amateur career in 2008: another NCAA 200 m title made him the third most decorated track athlete in NCAA history, and he won gold and silver at the 2008 US Olympic Trials.