The issue here is in the two mindsets on how to do ajax.  The clunky way (updatepanels) and a much cleaner way (anything that doesn't use updatepanels).  The DNN controls do ajax without updatepanels and do not do any postbacks, therefore wrapping them inside an updatepanel doesn't kick off the updatepanel.  You would need to have something inside your markup that causes a postback.

My recommendation is to not bother with trying to hack some clunky way of doing this together.  Instead I would simply allow one control to attach to/sync the other control's callback success event and update whatever text in whatever control on the client you want.  One of the samples I've included for the v.2.0 version of the controls demonstrates how this can be accomplished. http://webcontrols.dotnetnuke.com/samples/ClientEvents.aspx 

Jon Henning wrote One of the samples I've included for the v.2.0 version of the controls demonstrates how this can be accomplished. http://webcontrols.dotnetnuke.com/samples/ClientEvents.aspx

Jon, how do I get the source for this sample? I downloaded the source for the 1.5.3 version and it is not in there, but the dawntreader download is just the install .dll. 

The page above does not actually show the source?