I would avoid module communication as a rule - it is bad for SEO and prevents users being able to bookmark the current state of a page since changes made to one module by another module using the module communication system do not surface  to the URL level in a meaningful way.

I would instead strongly recommend that you maintain the state of the page in the URL using parameters as part of the query string.
If  you want to change the contents of the second module based on the selection of an action by the first module - do so by a url link action on the first module with values in the query string.

That way the user can bookmark the current state - and search tools can properly index your page - since they will walk the path of any URL's they find in the page.

With regard to your specific problem - the module communication interface does not have the ability to understand the concept of dynamically loaded controls. The interface is designed for communication at the MODULE level to MODULE level - as such you need to manage the sender / receiver as an interface of  the main module.

In the receiver on your main module you could then add your own code to trigger a receiver method on the dynamically loaded control.

Westa