Mainstream is a synonym of Conventional. Conventional is similar to Traditional. Traditional is similar to Classical. Classical is a synonym of Classic. 
you are likely to find Confusion in/at/on Conference. Conference is related to Business. 
Mainstream <--Synonym--> Conventional <--SimilarTo--> Traditional <--SimilarTo--> Classical <--Synonym--> Classic 
Confusion --AtLocation--> Conference <--RelatedTo--> Business 