A strategic shift by one of the subprime market’s largest players, Ameriquest Mortgage, has some competitors preparing to take advantage of what they see as a huge new opportunity to gain market share. But if Ameriquest is right, those opportunities may not be there. Ameriquest’s announcement last week that it had closed nearly 300 branches while shifting to a centralized retail origination model underscores a long-raging debate in the subprime market: how, exactly, borrowers