S2 Mic Engage Talkover mode?
That might be old school terminology, but what I want to do is lower the volume of the tracks when the mic is engaged, like they do on mixers. Helps people be able to hear you talk when music is playing, and also helps eliminate potential for feedback. Thanks. 
Mic ducking 
Don’t know if S2 or S4 have that option…only if you route it through a deck then use EQ to lower the volume.
I believe Denon is the only one to have that on a controller.
I see MIC ENGAGE button on the front panel of my S2… Not sure how it works since I never tried it but could be the thing.
Its just an on/off switch on the S2, plus you cannot record the signal unless you route it through a mixer. Just practise dropping your master by 26db when you talk
what Jester said…
Or maybe try high pass filtering the current track. I have the filter mapped to the gain knob…pushing it in disengages, so it could be an easy solution