eDimenional Audio FX Headset Problem - Works on PC but ...

I got this headset and it works fine on my PC with fs9, Skype, etc. However, when I try and use it on my Mac, the microphone doesn't work. I have 2 other headsets and they work just fine on both my Mac and my PC. I also tried the Audio FX headset on a friend's Mac, and it wouldn't work either. I contacted eDimensional and they were of no help. They said they had no Mac to test it on and knew no one who owned a Mac.So, I was wondering if there's anyone out there who has an Audio FX Headset and also has a Mac. If so, I would appreciate knowing if you can get the microphone to work on the Mac. If it works, then there's probably something wrong with my particular headset. If it doesn't work, then I suppose there's something non-standard about the connector being used by eDimensional to plug the microphone into the computer.I tried the headset on an October 2005 PowerBook and a brand new MacBook, both of which are running OS X 10.4.7. And yes, I did remember to go to the Sound panel in System Preferences and switch from the built-in microphone to an external microphone before testing. Indeed, this is my default setting since I have another headset that I use with the Mac and I was hoping to dispose of it and reduce the clutter around my desk.Thanks for any assistance in conducting this test - and also for any ideas that anyone might have as to why this headset doesn't work on the Mac when all the connectors are supposed to be standard connectors and other headsets work just fine.Robert