After finding your video on YouTube I started searching a little harder on google and found this forum post and decided to give it a go.
I just wanna say a massive thank you!!! this works a treat and quite easy to follow.
a few things I wanna add
I tried to make this as easy as I could for myself and copied this into a word document scaled up the pictures and printed this out, I used all the same coloured wires soldered to the pcb and it made following along that little bit easier.
one small thing I noticed the pcb diagram has a small error it has 2 up and down labels but no next and prev.
if i was to do this again id also desolder the plug of the off of the pcb while your desoldering the tactile buttons and run 2 wires (the little plug was hitting on the horn bracket and i had to grind a small piece off, also the wires are a smaller guage so using all the same size wires just makes fitting up that little bit easier.
my stereo swc wasn't a 3.5mm jack it was "key 1 key 2" wires. because this only has 2 wires you use key 1 for power and the ground went to the place my stereo was grounded.
cheers for making guides like this, making my daily that little bit better to drive every day!