Fannie Mae and Freddie Mac are still major forces in the non-agency MBS market, but their dominance is waning for the second straight year as competition for subprime and Alt A deals continues to intensify. A total of $55.17 billion of non-agency MBS were structured in securities classes comprised completely of conforming-balance loans during the first quarter of this year, according to the Inside Mortgage Finance MBS Database. That was down 14.3 percent from the… [Two data tables included]