which 2.1 audio system for the PC.

Look at the Yamaha 1000, which I have. It does 2.1 and 5.1. I use it as a 2.1 system without the sub. Pricey new, used it goes for about $200. Tons of inputs. Enjoy.

That isn't going to happen for $200. That being said, Klipsch Promedia (2.1) are often recommended on the computer forums.

A step up from that would be a used amplifier and some bookshelf speakers.

Adding a DAC and third party music player would be the next step up.

I am still researching, how is Audioengine A5+ Vs Focal XS2.1, which way I should go?

A desktop is a bad place to put speakers if you want good sound.