Hey that's my pic. So I'm guessing you found the website for the aux cd changer replacements. I love the one in my disco, but I'm a bit biased as it's my product. It's not a do it yourself project since there's a serial protocol handling the behind the scenes stuff along with a NLA 13 pin connector that I manufacture, but unlike the audio line taps that are all over the internet or the soldering mods to add an aux directly to the radio it does handle play/pause next and backwards through the head unit controls on certain iOS and android devices along with voice commands with optional microphone as shown here.
Waiting on the next batch of boards to arrive but they should be back in stock next week. Website is in need of an update, the full time job hasn't left much free time for that, but it's
www.flyinghorsesolutions.com
I have a circa 2008 iPod touch that's full that I leave in the car on random and it's like a never ending cd changer
It's got both the round and rectangular 13 pin connector so it should work with older range rovers, though I haven't tested it with the style radio that's missing the "prog" button.