Remote should in my opinion always be on when the radio normally delivers sound, or even without a key when I turn the radio on manually? Currently I have sadly installed a Hi/Low converter. This provides the remote based on the DC offset, I think.
I also used to run the line-out from the TDA7418 directly out. But this leads to noises when switching on and off when I use the remote from the radio. So I'm looking for a board/layout which also creates a remote. I found the following:
http://www.ertasvc.ru/parts/151.htm
(Its an OP482 so i guess it works like the boards in this thread)
Unfortunately I was not answered to my mail :/
Therefore I'm currently looking for a layout that can be printed in China to equip it myself :D