Have you tested this with both rear and front ports?
Is this issue only when trying to hear what you are saying into the microphone? i.e. Just wondering if you have any issues with just listening to things (i.e. music, videos, etc).
Also - I have to mention - but there are other threads in this forum covering audio/mic issues - it would help to browse through them as well.
I have a feeling that we need a stickied thread just for audio issues with the VI boards.
MOTHERBOARD: ASUS Maximus VI Formula (BIOS 0804)
CPU: Intel i5-4670k
HDD 1: Samsung SSD 250G 840BW EVO
HDD 2: Western Digital WD10EZEX 1TB Caviar Blue 7200rpm
RAM: 16gb (2x8) G. Skill RipJawsX DDR3-2133
PSU: Seasonic X-Series 750W 80 Plus Gold
GPU: Gigabyte GV-N770OC-4GD
CASE: Fractal Design Define R4
OPTICAL DRIVE: Pioneer BDR-209DBK
MONITOR: Samsung S24C300HL; BenQ E2200HD
OS: Windows 10 Professional
Other: MS Wired 600; Logitech MX 310; Sennheiser PC 151 & Logitech Z150