If you are not able to trigger an external synthesizer or sound module connected to the Oxygen's (Oxygen 8 v2, 49, & 61) MIDI Out port, either from the keys or from a computer sequencer, it is most likely because you do not have the MIDI Out from USB function properly set.

On initial power up, the data from the keyboard and its controls is sent directly out of the MIDI Out port.  This mode is shown in the display as “Int” (Internal).  When set to USB, the data generated by the keyboard will no longer be sent from the external MIDI Out port.  Instead, the data received via the USB connection to the host computer will be transmitted directly to the external MIDI Out port.  This mode is analogous to the MIDI Output port on a dedicated USB-MIDI interface.

MIDI OUT FROM USB
This mode is controlled as follows:

1. Press the Advanced Function button.
2. Press the MIDI Out key.
3. The display will show either “Int” or “USB.”