In case of a factory fitted CN+ the mic is in the lightdome. You clearly have room for (sun)glasses in the dome, so probably this mic is connected to your CN+.
the car is fitted with a cassette player, and can't see any signs of a phone holder being installed etc, was thinking that CN+ had been in but then some issues came along and one of the previous owners installed the cassette player instead
This is getting interesting, have you got a photo of the setup?
I have standard CN+ and these is now way I have place like that to put my shades in, I do wish sometimes there was some place other that to the front side of the gear stick.
Who would want to put a cassette player when after market radios with CD players can be picked up for next to nothing if you look in the right places?
I have actually seem very few Stilos with CN+, please a photo