PHP & MVC: Trouble dynamically creating appropriate MVC Classes

Question

I'm trying to build a CMS using the MVC pattern. The structure of my CMS is as follows:

->index.php: entry point. Contains the appropriate includes and creates the frontController which takes a router as it's parameter:

$frontController = new FrontController(new Router);
echo $frontController->output();

->router.php: analyses the URL and defines what the names of each Model,View and Controller will be. By default they are preceded by home, but if the url is of the form http://localhost/index.php?route=Register the MVC classes will be named RegisterModel, RegisterView and Register Controller.

if(isset ( $_GET ['route'] ))
{
    $this->URL = explode ( "/", $_GET ['route'] );

    $this->route = $_GET ['route'];
    $this->model = ucfirst($this->URL [0] . "Model");
    $this->view = ucfirst($this->URL [0] . "View");
    $this->controller = ucfirst($this->URL [0] . "Controller");
}
else
{
    $this->model = "HomeModel";
    $this->view = "HomeView";
    $this->controller = "HomeController";
    $this->route = "Home";
}

->frontController.php: This is where I am stuck. When I go to the homepage, it can be visualised correctly because I already have the default HomeModel,HomeView and HomeController classes created. But I created a link that points to register (localhost/index.php?route=Register) but the PHP log indicates that the appropriate Register classes weren't created by the frontController class.

class FrontController
{
    private $controller;
    private $view;

    public function __construct(Router $router)
    {
        $modelName = $router->model;
        $controllerName = $router->controller;
        $viewName = $router->view;

        $model = new $modelName ();
        $this->controller = new $controllerName ( $model );
        $this->view = new $viewName ( $router->getRoute(), $model );

        if (! empty ( $_GET['action'] ))
            $this->controller->{$_GET['action']} ();
    }
    public function output()
    {
        // This allows for some consistent layout generation code
        return $this->view->output ();
    }
}

At this moment I have no idea how to go about solving this issue. And even if I get the classes to be created in the frontController, is there a way to specify that the classes being dynamically generated should extend from a base Model,View,Controller class?
The default HomeView.php looks like this:

class HomeView
{
    private $model;
    private $route;
    private $view_file;


    public function __construct($route, HomeModel $model)
    {
        $this->view_file = "View/" . $route . "/template.php";
        echo $this->view_file;
        $this->route = $route;
        $this->model = $model;
    }

    public function output()
    {
        require($this->view_file);
    }
}  

Any indications on anything that might help me get unstuck or a pointer in the right direction would be much appreciated.

EDIT1:
I forgot to add a summary of my two issues:
1. I would like to understand why the classes aren't being created in the FrontController class...
2. Once created how would I access those classes? Answer is in the comment section. Using the PHP spl_autoload_register function.

Thanks All!