Audio conferencing system in recieve only mode problem

I have developed the audio conferencing system by using dialogic card DMV600BTEP & Dialogic API’s.

protocol :: ISDN

This solution is working fine. But i am getting a problem in my solution.

The Problem is as below ::

The Requirement :

I have created a 10 party conference. Now if a conferee presses a certain digit like 7 then my software part turns the mode of the confree to recieve only mode i.e.
he can only recieve(only listen).

After this when confree presses a certain digit like 8 then he can transmit & recieve both.

What i have done :

I am able to set the mode of the confree to recieve only when he presses 7. but when the confree is trying to press 8 so that he can transit & recieve i am not able to detect the digit press event.

As per the document provided by dialogic when a confree in NULL MODE(transmit & recieve) in a conference presses a DTMF digit it gives a trigger to my application but when the mode of the confree in RECIEVE ONLY MODE then hardware does not gives any trigger. i haven’t any trigger so i can’t do anything

I haven’t work a lot on ASTERISK just developed a few IVR’s with soft phones.

I just want to ask can i solve this problem using ASTERISK + DIGIUM card ?

If anybody knows how to solve the above problem then kindly tell.

Kindly reply soon.

Vishal Dhingra