Perhaps the most important component of a PC / desk audio is speaker stands and speaker isolation.
For a speaker to sound correct it has to be positioned, for example you have to get the tweeters in the area of your hearing. The other thing is when you lift a speaker from the desk it changes the bass and how the speaker fills the room.
There is also optimum positioning of the left right speakers from each other. If you widen the gap between two speakers it increases bass, close the distance between the left right speakers it will highlight higher frequencies. You should be positioning speakers so the vocal is central and sounding back behind your monitor. After this you should toe speakers in so the sonics of the overall sound is balanced.
Another thing to discover is the minimum distance a speaker can be from the wall. Generally you want the speakers as far back as possible (i'm assuming your desk is against a wall), however there is tipping point where the sound quality will suddenly drop off, so normally you would place the speakers just ahead of that point.
I'm referring above to under 1 cm adjustments in distances and height, and small 5 degree changes in toe angle. These small changes are all it takes to adjust the sound. This is why you need proper deskstands you can adjust and lock in place.
If you have a sub, that needs placing so it's sonics are working with the main left / right speakers. Again it's positioning of the sub, how far forward / back to the wall. Lifting a sub on a isolation platform again helps tighten sound.
The other thing important is speaker isolation foam as it stops resonance into your desk that will muddy the sound. To help understand resonance place your hand flat on your desk with music playing, if you can feel vibration that is resonance that's reducing your sound quality.
And regardless if you have a £100 setup or a £1000 or more setup the above all applies. This is why a budget system that's setup correct can sound better then a incorrectly setup more expensive setup.
And none of this is expensive, speaker isolation foam can be as little as £10. Adjustable desks speaker stands there £20 upwards. Subwoofer isolation stands are more money, however you can at first use polystyrene foam to lift and isolate a subwoofer. After this it's just your own time to set everything up.