I'm making a musical instrument which contains four Teensy 3.2s: one which is connected to the computer via USB, and acts as a master MIDI device, relaying messages out from the 3x serial ports. I'm using quad audio boards for multiple audio inputs hence the multiple teensys.

My question is, since these microcontrollers will all be within the same physical space in the instrument, can I simply connect TX from the master to RX in the slaves without the standard optocoupler circuit used for DIN connectors? Would there be any dangers / disadvantes in doing so?