Windows 7: Headphones/Speakers not simultinous (IDT)

Okay, so I would like to play sound on both my Headphones (logitech) and at the same time als on my speakers.

I don't have Realtek, so I can't just click in the Audio Manager "Play sound on both output thingys"
I have IDT with HP Beats audio as manager.
I know you can do this with the StereoMix playdevice and I have tried some stuff but nothing worked and at some moment my headphones started making a squirrel being tortured sound.

Okay just managed to fix it, no idea how thou.
In case anyone else has problems this are my settings:

Speakers: main device
Headphones: communication device
Stereomix: Listen to enabled, listing to communication device.
Options for volume control
Devices that play sound: unchecked (most solutions I saw said that it had to be enabled?)
Standard communication device: unchecked
Sound devices:
Speakers:checked
Headphones: checked.

Can anyone explain why this works?

Where are these settings in your second post? In device Manager?

If you right click on the volume tray symbol (right down in the bar).
Then click options for audiocontrol (or something like that, probably the lowest option)
In that are most settings I think. Also go too Audio devices (in the same menu) and there are the rest of the settings.