Usually one-way audio is a routing issue. Have him place a call and then look at the audio stream traffic. I would imagine the return traffic doesn't know how to get back to him. Could be a NAT or routing issue.
I know with MeetingPlace 6.X, there is no need for CallManager. The audio server (8112) is a blade server and the blades can handle the trunking. Im not sure with 7.X.