Quality Voice Communications Possible?

A friend and I both have fairly adequate systems for FSX (he has a Nvidia 8800 GT card on 3 Ghz sys, I have a Nvidia 7900 on a 2.5 Ghz system) and are trying to setup quality voice communications in Multiplayer that is understandable and with good volume. It seems that most of the time our voices are muffled, or too low, or non-existent. We are both using Sennheiser headsets .. his audio onboard chipset is SoundMax and mine indicates AC97. We've gone through the setups, searched online and played with the settings until we're blue in the face. My friend has tried 2 other headsets to no avail. We DID get one acceptable session .... the very first time we tried, but then his system locked and corrupted his sound drivers and we reloaded ... but since then, mostly poor quality. We end up going to cell phones with headsets. I haven't been able to find much info through Google ... but maybe I've just missed it? I'm always the Host if it makes any difference? Any ideas or help appreciated. :) 
