My understanding ... is that the TTL interface is how the Arduino talks to the USB device
I'm wondering how others address this need?
There's a bit-banged "software serial" approach (I'd use this one)
With an Arduino MEGA it would make a lot of sense if there was some way of specifying the serial port when doing a Serial.begin(), but the Serial object is predeclared, which would make it impossible to have multiple serial streams on it even if you could point it at different ports
SerialClass Serial, myLCD, my328; Serial.begin(9600,COM1); myLCD.begin(9600,COM2); my328.begin(9600,COM3);