A yes, the registry issues and your sound card. lots of new equipment have sigmatel or idt or realtek sound drivers. , most have the configuration controlled via the registry. some have the option installed in the registry but just turned off at the sound card utility.

open your control panel. select the sound icon and that will present you the screen for configuring your sound card.

it's not perfectly clear that you are tryinfg to use stereoin as a recording source like whaty your hear or like stereromix.

Your registry may be configured to support these options, or it may not.
the sound control tab that you are looking at should indicate that. go to the recording tab and investigate your options.

If the options are not vissible then they may need to be modified in your registry. that's not always simple and not for the faint of heart.

You could also try to find the latest or alternate drivers that already have te function installed.

let's take it one step at a time. look in the sound tabs from the control panel.