Factory Head Unit Wiring

[litldrumrboy]

Can anyone shed any light on something which is causing some serious headscratching?

I have the standard radio with RCA aux input, does anyone know what the various pin outputs are for on the rear?

I have the main block which is I assume power etc and speakers which are all quite large pins, there is then also a section with much smaller pins which I guess is either the dash display, steering wheel control and aux, but then the loom also has another white connection block that has three wires going into it but the rear of the stereo has no pins for this to connect to so whatever this is for is not supported by the standard stereo, wondered if I purchased another factory stereo with Bluetooth and USB if this would mean I wouldn't have to change the look but would have everything I needed (handsfree calling/USB charger/music streaming), could the white block be either the CD Changer or Hands free mic?

I don't know where to look to check if there is a spare connector where the CD changer would be or where the internal mic would be for handsfree calling.

Thanks for your help (hopefully).