?VoiceNumber in the MIDIOutputEvent will be set by the StepSequencer rather than by the Replicator.
You could use a different variable in the MIDIOutputEvent, say ?myVoiceNumber and place a Script between the Replicator and the StepSequencer. In the Script you can set the value of ?myVoiceNumber to be the value of ?VoiceNumber from the Replicator. For example, in the Script field of the Script, you could use
orchestra first start: 0 s myVoiceNumber: ?VoiceNumber