2 loudspeaker on one pc?

If you have more than one audio output source, and your software supports outputting to specific sources, then yes.

I would investigate sending HDMI audio to your screen playing the videos, if possible, and sending audio from your games out the sound device on the motherboard.

In general I thought the answer of multiple audio sources would be NO.

In "Playback Devices" you need to select a default audio source which can be:
a) Realtek onboard audio
b) HDMI from graphics card (or part of CPU's iGPU via motherboard)
c) Sound card

I can only choose one source as default.

Now, I'm not sure what your goal is here. You want gaming sounds on one monitor (with speakers) WHILE movies are running on another monitor?

Now again this likely has to be via HDMI as the sound source. It can output two different video streams but you'd have to experiment to see if the audio is separate or just the same on both. No idea as that's not something I've heard people doing.

I have heard of simply playing MUSIC while a game is running and that's possible though it's usually just done through the same source and on the same speakers.

Windows can output to as many sound devices as you can physically attach, provided the software used to output the sound can specify which sound device to output to.

The problem is that, most games and general use software is only written to output to the default sound device.

Software such as Windows Media Player, VLC, and commercial media playback software allows for the user to specify which audio output to use. Since you can't rely on your games to give you an audio output selection, expect to set your default audio device to whatever you want the game to use as it's sound source. I would assume the motherboard audio or a sound card should be sufficient for gaming. Most decent media playback software can target a specific audio device, so personally I would shoot for HDMI audio out through the display's speakers, for the media playback. Since primary focus will be on the games being played, I tend to use the better audio output, such as through amplified speakers for that, and the half ignored audio I relegate to the inferior display speakers.

Agreed (bigpinkdragon286),
However, I'm not sure if you can choose separate HDMI outputs. He mentions two monitors.

I have no idea WHY you'd want a movie and game playing at the same time, but it may work something like THIS:

#1 - setup default Windows audio playback to HDMI and play via the monitor speakers (or passthru to desktop speakers), and

#2 - use onboard (i.e. Realtek), sound card, or USB solution. Go into the MEDIA PLAYER (i.e. K-Lite using WMPC-HC) and designate the source:

WMPC-HC-> settings-> internal filters-> audio renderer

(since again, I'm guessing you can't use multiple HDMI outputs, if so you'd need to place the desktop speakers on either side of this monitor)

I'm not confirming this works, but I think that's PROBABLY how you'd do it.

I suspect I understand, as it's something I do often. HDMI audio outputs work like any other audio output devices. I can watch a movie, TV show, YouTube, etc. while I'm playing a game. It's not something I do so much with some 1st person or competitive games though, as the video does become a distraction, but if playing an offline RPG or something with a lot of in-between action, the video gives a nice distraction from the otherwise boring parts.

One reason I use the better amplifier plus speaker setup for games is so I can have surround in my games. I only swap things around if I'm watching a movie that I want surround for, or when not playing a game. When gaming, I generally don't care if TV shows or what have you are in surround.