I just posted my recorder app that does the same thing. I use NAudio WasapiLoopbackCapture. it's written in C#

Ah yes, it's a good idea to record microphone and system audio to different files but I ruled against it for simplicity's sake. I wonder how you deal with offset, esp. when the mic comes from a Bluetooth headset? I added an offset option in the config file as this can be up to 2000 ms (2s) in my tests! Also, a console app may frighten the non-technical, casual user?

But anyway, great minds think alike I guess! ;-)