I'm not certain what problem regarding the headsets that this thread is trying to address. But I do know one thing, the N900 has a problem when using certain headsets, some wired headsets sound ridiculously low and soft when using it with the n900.

I created a script that fixes this problem which can be found here.

With this script you can use any headset with the N900 and you won't have that low audio issue. I'm using some cheap $15 headsets with mine and they sound great (as in loud and clear)...I also tweaked the bluetooth headset quality a little.

I don't have any headets with mic, but I have tested some random wired headsets that have volume control on em and so far they all worked with my script.