If you are happy with the sound you already have, there is no point in getting a sound card.
Most sound cards these days are little more than ADCs/DACs with a PCIe (or USB2/3) interface so you would gain absolutely nothing from overclocking one of these even if you could. These usually need less than 5W and do not even require a heatsink.
Thanks. I now know that getting a sound card isn't something I'd want to do. I do think I will buy a slightly better headset because I do want a little bit more from my headset.