According to "Intel Driver Update Utility, the audio driver was "current", version 6.0.1.6914.
I did try both front and back connections. The outcomes were the same.
The BIOS version was KCH7710H.86A.0110.2013.0513.1018, based on Intel Desktop Utility. System Information showed the same thing.
Should I roll back the BIOS? Can you test the MB in your lab?
Thanks
PS. I saw quite a few posts similar to my situation before I posted mine. The first suggestions were pretty much the same, checking/updating the driver, which I did that already. On the other hand, I don't remember I saw anything from in release note(s) about microphone issues.