I have read several threads that attempt to troubleshoot this issue, and none solve the problem. The frustrating part is that the solution is so simple. Corsair staff, please post one thread with the following fix.
Soft reset your headset. Now test the sidetone control in the iCue software.
CORSAIR STAFF, this is a known issue, and it is really really frustrating. Please post real guidance, and not another suggestion we update, reboot, or post ad nauseum configuration details. A simple headset reboot, or soft reset seems to be the real solution. So please open all posts on this topic, and add simple guidance pinned to the top that details the soft reset process, and suggests that as the first troubleshooting fix. Oh, and while you are at it, since this is a known issue, how about resolving the issue once and for all with an actual update to your software and firmware that permanently fixes this? Just say'n. Thank you.