If you're not doing anything high end there will be little difference, and if you use an optical cable or HDMI for your audio output then your audio will be digital and a sound card would do basically nothing at all. There are some cases where a sound card can still be useful for optical audio but HDMI is the new golden standard for high fidelity audio, though not all HDMI is equal. The 4K HDMI spec specifically is the new golden standard and to really utilize it you would need to be running HDMI to a 4K certified stereo reviver as nothing else would reach that level of audio fidelity.
So basically, HDMI is replacing the need for a sound card. Personally I think quality 4K receivers are still pretty expensive and therefore I use a sound card to connect to my receiver via analog for 5.1 surround. I tried 4K HDMI for a while with a $300 receiver and it did sound really good but it caused some glitches with my TV when gaming that caused me to return it and instead use a quality sound card for analog.
i7 7700kK @4.2ghz
16GB DDR4 3200mhz
GeForce 1080 Ti