We hope to have specific help for Logic Pro Users. The Montage is a MIDI keyboard with a built-in audio and MIDI interface. You can choose to use the Audio interface or not. While there are things to consider with setup, there is a lot of help. In general, doubling is a matter of routing signals from the Montage to your speaker system as normal. That is, from the synth itself to the Main L&R outputs. Then you have a path of audio that you are routing to the computer via USB. When you are using the Montage as your computer's audio interface, it returns audio to the the Montage but this time the Montage is acting as the audio interface (routing the signal, again to the speakers). One is called the DIRECT Monitor signal, the other is post the computer (the latent) signal.

You can choose to monitor (listen) to one or the other. Hearing both means you are routing signal both to the speakers DIRECT, and also through the computer.

If we use the old school analogy of a tape recorder... in the studio the engineer opted to listen DIRECT to the signal of the musicians as they played. The recorder (back then, magnetic tape) as several milliseconds behind the live musicians (caused by the distant between the record head, and the playback head) so you monitored the musician direct. On playback the engineer was always relieved that the recording actually happened. And playback was to verify the data was recorded (sure the meters say it was recorded) but you don't really know the quality until playback.

Here in the digital age, it is not the distance between the record and playback heads that causes the delay in the recorded signal, but the fact that computers have to receive, time stamp, position, and then retrieve data in order to document and playback. It is still delayed, but the reason is high tech. You can opt to mute the returning audio during record or you can opt to turn the DIRECT MONITOR OFF in the Montage to eliminate the possibility of monitoring both signal paths.

It is your choice. And is a choice you must make based on what you are doing. There are times when you are processing signal in the computer and you want to hear that processing (but that is the rare occasion... most plugin effects are designed to be used "after the fact" not during real time record). With all the boutique processing on board the Montage, you might just opt to monitor the Montage Direct and mute the computer return until "playback".

Hope that helps. I am not a Logic Pro user so I cannot tell you exactly where to go to make these settings - but they are similar in all DAW. It is a matter of setting made on the Track for Monitoring. The DIRECT MONITOR function in Montage is found on the AUDIO I/O page in Utility

Press [UTILITY] > "Setting" > "Audio I/O"
Direct Monitor is responsible for sending the Montage directly to the main analog L&R outputs (ON).
Direct Monitor OFF means the at the audio will only travel out via main USB L&R outputs to your DAW, the Monitor function of your DAW is in charge to hear the returning audio.