CREATE TABLE table_name_67 (opponent VARCHAR(255), date VARCHAR(255), type VARCHAR(255), round VARCHAR(255))
Which Opponent has a Type of tko, and a Round of 2 (6) on 2006-09-20?
    
SQL: SELECT opponent FROM table_name_67 WHERE type = "tko" AND round = "2 (6)" AND date = "2006-09-20"