Все гораздо проще:
..... array( "sort" => "field1 DESC, field2", "dir" => "ASC", ),... // result ->sortby("field1 DESC, field2 ASC");
..... array( "sort" => "field1 DESC, field2", "dir" => "ASC", ),... // result ->sortby("field1 DESC, field2 ASC");