Do you want 5.1 digital surround? I think that was your main question...The PC decodes the digital signal and outputs it to analog, the 3.5mm jacks on the sound I/O section of your PC. This can be done rather cheaply. Using the analog outs of your PC and amplifiers like this (below), you can power your speakers and even upgrade to better ones later. You'll need 3.5mm to RCA cables to plug into your PC's surround jacks. Depending on your PC's sound card, you should be able to use 5.1 or other surround modes, which can be configured in the speakers section of your sound software's setup section.
Examples:
https
/www.parts-express.com/lepai-lp-2020ti-digital-hi-fi-audio-mini-class-d-stereo-amplifier-with-power-supply--310-3000
https://www.parts-express.com/audtek-35mm-to-rca-stereo-audio-cable-6-ft--181-434
3of these will power 5.1 speakers, using one channel of an amp for center, the other channel for SUB, one amp for L and R, the 3rd amp for rear surrounds. $75 plus shipping.
This amp can be BRIDGED into MONO for 150W to a sub for real bass! Be sure your speakers can handle the power.
https://www.parts-express.com/dayton-audio-apa150-150w-power-amplifier--300-812