Don't search for computer speakers, just look for normal speakers on which I can't help out too much on. Unless you want to invest into an expensive sound card, you probably should go for an AV-Receiver which transmits the audio through HDMI as this will give you the maximum quality depending on the supported formats. I have a sound card -> old school amplifier -> speaker setup. Basically it is your choice where the digital to analogue transformation happens, whether through a receiver or sound card. A sound card does have the massive advantage of providing virtual headphone surround sound (yes on stereo headphones, and no, this is really working) which receivers typically don't have, because reasons and it will provide you with a massive immersion boost. And no onboard sound is not comparable, even the best one is a clear step down.