Should mention, there are ways for you to talk to second PC through the host if you desire. At least by simple Serial...
That is we support many of the USB to Serial adapters (FTDI, PL2303, CH341, CP210).. Then depending on your adapters, you can maybe either setup to hardware Serial port on the second PC or use another USB to serial adapter that connects up the one on the Teensy...
Of course you could in this case also bypass using the USB to Serial adapter on the Teensy and simply connect up to Hardware Serial pins.
Hope that makes sense.