Instead of passing string to view directly, you should use sce.trustAsHtml to pre-process the html.
$scope.bindHTML = $sce.trustAsHtml(item2._unparsedString);
Then in your view template, use ng-bind-html to handle html binding.
<div>Preamble : <div ng-bind-html="bindHTML"></div></div>
As you mentioned you have an array of object, it's not that easy to cast them in your controller, you can bind $sce to your $scope then call trustAsHtml in your view
So in your controller
myapp.controller('mainController', function ($scope, $http, $filter, $sce) {
   $scope.$sce = $sce;
...
}
Then in your html view
<div>Preamble {{$index+1}} : <span ng-bind-html="$sce.trustAsHtml(item1.Preamble._unparsedString)"></span></div>