No sound through headphone jack on 2014 Mini.

I have a late 2014 Mac Mini with OS 10.13.4. It is connected to an ASUS LCD monitor with an HDMI cable. There is sound through the monitor's built-in speakers and headphone port. No sound through the Mini headphone port. This was not the case until recently.

I’ve had a Focal iCub powered subwoofer connected to my computer with a 3.5mm cable connected via the headphone jack. The subwoofer also amplified the sound and supplied two built in wall speakers. With this configuration all the sound went through the external speakers and there was no sound through the monitor's built in speakers. This was the configuration I used with the ASUS PB258Q from the time of purchase (12/21/16) to present. The subwoofer (several years old) recently had problems and I discontinued using it. I think it might have had a power surge which burnt the speaker coil. Don’t know for sure.

Since that incident there is no sound through the headphone jack. Only the monitor connected with the HDMI port can provide sound. As an experiment I connected the monitor to the computer via a mini display to DVI connector. There is no sound through the monitor; either through the built in speakers or headphone jack. There is only a low frequency humming sound through the computers’ headphone jack. I understand that DVI signal doesn't cary sound, only video. But with a DVI connection to the monitor there should be sound through the Mini's headphone port.

Is it possible the damage to the speaker connected to the Mini also damaged the headphone port? Seems like it to me.

How do I get this repaired?