Booker Edwards' External MIDI Advanced course teaches you all about everything external in Logic Pro. Not only do you learn about managing multi-timbral instruments but Booker also totally demystifies your new best friend: the External Instrument Plugin.
In the video tutorial below, Booker shows how to sets up drums in Logic X in order to process just the snare with an external hardware processor, in this case the Art Pro VLA 2 channel hardware tube compressor.
The I/O plug-in acts as a physical insert in Logic's signal flow. Basically, you can use it to make a serial connection to outboard hardware processors. Booker shows breaks down in detail how the signal flow works, both going out from Logic to the hardware processor and then back into Logic, all via the I/O plug-in.
The next video in the course shows specifically how the snare is processed using the outboard compressor.
Other videos in this advanced course on External MIDI in Logic Pro X show how to synchronize Logic Pro with'¦ ahem'¦ Pro Tools'¦ and much more too.