BenQ SW2700PT - Unable to bypass monitor speakers in order to use mac mini audio optical output

[rainforest1]

I just bought a BenQ SW2700PT. It is connected, via a Displayport cable, to a late 2014 mac mini. The headphone jack on the mac mini also doubles as an optical digital audio output. Before I purchased the Benq I had been using the optical output on the mini to connect, via Toslink, to a digital to analog convertor that is then connected to my audio system. Unfortunately, I have not been able to find a way to bypass the Benq monitor's speakers and use the optical digital audio output on my mac. Since I have a large collection of high resolution digital music I like to listen to, this has been a huge disappointment. Also, the controls for Audio on the monitor are greyed out. Any Help much appreciated!

 

[rainforest1]

Regarding my above post concerning the Benq monitor speakers I looked at System Preferences, Sound on the mac. Under "select a device for sound output" the only devices now listed are the built in Internal Speakers (on the Benq). Looks like installing the Benq has resulted in my losing all previous output options including the headphone/digital optical output on the mac mini. How I get these options back, I don't know.

 

[rainforest1]

I contacted Apple Support and they suggested that I try a different cable other than the Displayport cable provided. I shouId add that when I was using the DP cable, a Menu on the my Benq for audio was greyed out. I had seen a youtube video that showed a PC user using the audio control to mute the built in speakers on a different model Benq but took this to mean that we Apple users were being mistreated. But voila, after installing the HDMI cable the Audio control was visible and I was able to mute the Benq’s internal speakers. This fixed the problem of the mac mini’s earphone/digital optical port being shut down and unusable. Great to hear music again. Many thanks Apple Support!
Additional Info: Despite the above I noticed today that the DP mini to DP cable is damaged. The metal connection on the larger DP cable end flops around a bit in it's plastic housing so now I'm wondering if it connected poorly to the monitor and possibly caused the greying out of the Audio Setting. Maybe a little farfetched, but possible. Also, I'm thinking that the HDMI cable I purchased (the cheapest Monster) is not producing colour and resolution that equals that of the Displayport cable. This is supported to some extent by some techies that say that Displayport beats out HDMI at 2k (my monitor - 2560x1440) and 4k. So, I plan on purchasing a new DP to DP mini cable to test this out....