I was hoping you guys could help me with my friend's installation. He has a 1999 Miata M2 (2nd Generation Miata) with the stock stereo. We did some research on whether the Rio Car could be a slave to the stock radio. It seems there was a famous website that detailed how to easily modify the stereo to accept AUX-IN. However, the links are broken and I haven't been able to find them anywhere (even in Google's cache).

Anybody know about doing this install? Here's a link to stereo specifications from Miata.net.