For the direction, you'd need to get the direction the player was facing with getDir, then use the trig guide in the Editors Depot to help you figure out the angle between the player and the opfor group, then find the angle between the two and call the appropriate sound file accordingly.
Sui's mission "The Black Gap", currently on the beta testing board, has a Command Interfact that includes this feature. When one of the squads under your command makes contact with the enemy, they call out the range and direction. You could unpbo the mission and find out how he does it. Remember to ask permission if you want to borrow anything.