Columbus, add a sub

Hi All

I have searched and could not find anyone with a step by step guide in adding a sub/amp to the Octavia with the Columbus head unit.

I have installed subs into car before and added it to aftermarket head units with sub pre outs.  I see that i need a line out convertor?

recommendations on which one is suited with use with Columbus? 

how do I get the Columbus unit out? 

earthing and getting power to amp is easy for me, but struggling with the whole line out, thing 

any help much appreciated. 

Octavia 2014, Columbus H42