Complex sentence: He originally started off on K2 (sports) skis, but then switched to Fischer through the 2002 season, switched to Rossignol for two seasons (2003 & 2004), then Atomic for the following two (2005 & 2006).
Split into simpler sentences: He originally started off on K2 skis, then raced on Fischer through the 2002 season. He switched to Rossignol for two seasons (2003 & 2004), then Atomic for the following two (2005 & 2006).