So I take it you actually have a 4.1 system? That is, you do have a sub-woofer?
Your Audio Device should be the "Realtek High Definition Audio [WASAPI]" option, and you should have it in Exclusive Mode under Device Settings (Open device for exclusive access). When in exclusive mode the settings in the Control Panel and the Realtek Utility should be making no difference, as MC is controlling the device directly. Also, when using the Control Panel audio tests you are using Direct Sound, I believe, and not WASAPI. I think the Realtek Utility would be the same, using Direct Sound. When you use Direct Sound, Windows is going to interfere with the sound, and you don't want that.
So, if you are using WASAPI Exclusive mode, with the Output Format under DSP settings set to 5.1, and the checkbox "Move center to front L/R" is ticked, and still you aren't getting surround sound, then you have a channel mapping issue.
I'm no expert on which channels are mapped to where for the different formats, but there have been some discussions about that in the forum. See if you can find them with search.
The solution is to use the Parametric Equaliser in DSP settings.
Not only can you move channels around with that, but you can add a "Mix Channels" effect to "Add Centre to Right" and another to "Add Centre to Left", which means you won't need the checkbox "Move center to front L/R ticked. That should give you more control, including the ability to adjust the volume of the resulting mixed left and right channels, by dB adjustments. Usually you will need to add a negative dB adjustment when mixing channels. That way you won't muck up any Room Correction you are using. But you could leave the Mix volume alone and just use Room Correction to adjust the front speakers for their increased mix volume.
Then add an "Order Channels" effect to move the surround channels where you need them to be.
As you can see in the attached image, the surround channels are in positions seven and eight by default, after the Rear Left and Rear Right of a 7.1 channel setup. I suspect that your surround channels are in positions five and six on the motherboard audio outputs.
BTW, to test each channel, see if you can find a test 5.1 channel video on the internet, or search for links to them on the forum. You should be able to find videos that will play one channel at a time, so you can check the audio is coming from the correct speaker.