Can't see Stereo Mix on Dell Inspiron 7520

Hello

I know this is an issue going on for years and I've googled and read a lot of forum posts about this topic but I still can't figure it out.

I have a new Dell Inspiron 7520 and I want to use the Stereo Mix feature so I can record audio coming out of my Conexant SmartAudio HD soundcard.

I tried opening the driver .inf file and un-commenting these three lines:

HKR,%EPattributePath%\EpSettings\StereoMixEnable,Enable,1,01

HKR,%EPattributePath%\EpSettings\StereoMixEnable,MixAssocSeq,1,E0,E0

HKR,%EPattributePath%\EpSettings\StereoMixEnable,MuteGainSettings,1,00,00

I then go back into device manager and re-install the Conexant driver by browsing to the location of the .inf file I just edited (by removing the semi-colon comments). But I get the error message: "Windows found driver software for your device but encountered an error while attempting to  install it - Conexant Audio HD - The System cannot find the file specified." Right before that I notice it says the driver is not signed which might be a problem as I have 64-bit Win 7 Home Premium.

Any advice greatly appreciated.