So far the troubleshooting nightmare continues.

I've isolated the problem to simply that my monitor's built in speakers are getting priority over my 5.1 speakers. The monitor's speakers work no problem, but the 5.1 that I bought can't work with it even if I mute the monitor. I've also brought this to the shop to confirm, and they found that the 5.1 works with a different monitor.

How do I disable the speakers in my monitor so that my 5.1 can work?

nevermind. finally fixed it lol

How'd you fix it?

it wasn't my monitor after all. my avr apparently couldn't handle the power of having my cpu, monitor, and speaker system at the same time. so i just plugged the speakers into a different socket.

it's weird coz when i plug the speakers into the avr, the light is actually green, meaning it's on, but there's no sound. when i plugged it into another plug, suddenly the sound came on. weird.