How could you structure and route modules in a MVC?

Question

I'm building a MVC where everything is a module. This will allow me to separate collections of objects like forum and user modules to further organize my MVC.

/blog
    /controller
    /model
    /view
/user
    /controller
    /model
    /view
/forum
    /controller
    /model
    /view

I currently map routes for something like forum/edit/34 to /forum/controller/edit.php which contains the Forum_Controller_Edit class. (This is slightly different from the standard approach where all actions are methods of a controller Forum_Controller::edit()). This allows me to separate all the individual "actions" of a controller into their own files so I don't have to manage large controllers with 10 different actions.

Anyway, here is the problem. Suppose I want to add new controllers to a module. For example, lets say I want to have forum topics (forum/topic/view/34). I could create a new "topic" module.

/forum
    /controller
    /model
    /view
/topic
    /controller
    /model
    /view

But then 1) I would have to use URL like /topic/view/ instead of forum/topic/view, 2) I would have separated related components (topic should be a part of the forum module), and 3) I would now not be able to create a general "topic" module for something like content nodes if I wanted to.

So how can I build a modular MVC while allowing multiple controllers (with multiple actions) in each module?

Kohana Framework decided to implement a HMVC to solve this problem. However, that results in many is_file() checks to find the correct location of the file you wish to load. I/O checks are very precious on commodity hardware so I don't consider that an option. Also, it is not apparent which version of a class is being loaded which can lead to confusion when working with multiple classes with the same name.

I would like to find a solution to this problem that does not involve pre-setting paths or checking folders for the right class. Yet, of the last 20 frameworks I looked through they don't seem to have a good answer to this universal problem. Anyone have some ideas?

Routing Update

If I was to implement routing, how would it work? How would I handle first (/forum), second (/forum/view), and third levels (/forum/topic/view)? How would my routes know the difference between a third level route and a second level route with a parameter? In other words, which of these would my system try to do? (Given the URI "forum/topic/view/34")

$controller = new \Forum\Controller\Topic\View;
$controller->action('34');

// or
$controller = new \Forum\Controller\Topic;
$controller->view('34');

// or
$controller = new \Forum\Controller;
$controller->topic('view', '34')

Routing Update 2

Taking Kyles advice I decided that ALL controllers will need a route set which will allow me to define which of the classes above the URL path "forum/topic/view/34" routes too. After all, EVERY URL is important and should not be based on the filesystem structure you have in place. I believe he is right in saying that the URL design deserves more attention than we often give it.