Perhaps another option besides getting a different headset/louder mic, is to use Mumble for voip if you aren't already. Me and my teammates switched over to it specifically because of it's auto-leveling feature, where it adjusts people's volume so that everyone is at the same (or nearly the same) volume. I had a Zalman in the past, then I got a logitech desktop mic, and then a Blue Snowball mic, and with every one I was still having people tell me that I was quiet. Ever since we switched to Mumble though I haven't had any problems.
Good luck with your search!