I think AEmitters can have emitters stuck to them... If so, putting another emitter on your projectile would fix that. Just have the new emitter do your sound while the projectile does its flight thing.
Code:
AddEmitter = AEmitter
CopyOf = Sound Maker
InstanceName = Rocket Sound
ParentOffset = Vector
X = 0
Y = 0
And are those emitters you spoke of
emissions, maybe? If I remember correctly, the coalition rocket is an emitter, not a MOSRotating with emitters stuck to it. In that case, the burst settings are handled by the projectile, so you needn't worry about the other emissions setting off the burst.