My girlfriends line in is a very hot input. I use a 10db pad I had lying around for recording live shows. Looks like m-audio discontinued it but you can still find it online. works like a champ and is transparent sonically. On the other hand the line in on my car is very low. anyway it works well so there is a suggestion.
https://www.google.com/webhp?source....,cf.osb&fp=784d899c8f80c925&biw=1366&bih=677
https://www.google.com/webhp?source....,cf.osb&fp=784d899c8f80c925&biw=1366&bih=677