It is not true the extender hide the events from the control. If you put a break inside your routine you may found the event handler code is running. If you want to update a control on a async postback which is not inside the update panel then look at this link
http://msdn.microsoft.com/en-us/magazine/cc163354.aspx[
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"My users need to see the changes immediately without having to tab or press enter"- How the control knows your user finished entering chars? There should be a way to tell it right...enter, tab, blur event etc.,