I'm seeing the same problem here, but slightly differently. I've got two 6700's running the Helmi WM6 ROM, and one has the same problem you describe. The other was set to 1x mode when I loaded the ROM, and now can't be switched back to hybrid. It looks like it's the switching that's not working, and not the modes themselves...
I suppose if you have the time and don't mind hard-resetting a couple of times, you could revert to the stock ROMs, switch to 1x mode, and then install WM6. Assuming I'm correct about how I got into this state, that should work. Of course it leaves you in 1x mode, without the ability to change it...
