headset for business???

Hi there, i need your help. We have a lot of iMacs here in the company and use Skype/Lync/GoToMeeting for internal and external communication. Obviously we use headsets, and here it comes. Some Macs run natively Windows and have no problems with USD headsets, myself and some others work with Mac OS, and we tried several different headset types, cheaper and more expensive, but non works:

• USB heads sets, listening is not problem, but speaking is. after few minutes of talk, the voice becomes robotic. we can still hear, but the other person can not. The audio quality gets worse and worse up to the point where no word can be understood. Unplugging the USB cable and replug solves the problem for another few minutes, and then it starts again. We tried different modes from Logitech, and also other companies, still the same
• Bluetooth: it's the opposite. Speaking works, but listening is bad. immediately the sound quality is low and brake up. Listening to music is fine, but with any VOIP device it's really bad. in the MIDI settings i can see that it switches to single channel 16BIt 8KHz as soon i pick up a call or try to make one
• external custom wireless: some logitech headsets comes with a proprietary wireless USB connector, a little thing that you plug into the USB port and works as radio bridge. Such headsets works, both for speaking as for listening. However those are the most expensive, are heavier and you need to deal with battery life, or like in my case have the charging cable plugged in.
• original iPhone EarPods: those works, no doubt!! however, as when they are plugged in, all audio is routed to the earphones, i cannot hear my Skype/Lync ringing, or any other sound, unless i keep the earphones on the whole day.

bottom line, i'd like to know wether there is an officially supported headset, preferably USB, that works for business (phone calls, conference calls, etc.). This all works if Windows is installed, which makes me feel bad just writing about it.

I've contacted apple support on this and they sent me to Logitech. I've contacted Logitech, and they sent me to apple, as the Bluetooth works with iPhones, so it must be an iMac problem. I have 5 different headset on my desk, and non works as it should.

I've found a lot of posts abut the robotic sound problems with USB headsets, but no solution. I hope i can find here a good advice. Please don't tell me i have to install Windows.

thanks!

ciao

marco