I want to receive a stereo balanced audio signal and feed it into the stereo microphone inputs via my motherboard's header pins.

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/qCyPU.png

I added about a 30db reduction in gain which looks good on the scope and audio sounds great from headphones/speakers.

But here is my issue:

If the opamp is not powered, I will be sending the hot signal into my L/R mic inputs without gain reduction and I am afraid that will cause damage to the motherboard. So I need to attenuate or mute the signal if no power is applied.

My two ideas are:

1) Use a JFET to mute the circuit like shown here: https://sound-au.com/articles/muting.html#s2

or 

2) Use a unity gained design for the differential amplifier then just have a voltage divide at the input of my circuit to reduce the level.

My question is: Do you see issues with these approaches and is there an alternative approach you would suggest?