Nope. Your audio quality is already very good, the only reason to upgrade would be if your mobo’s audio out can’t power your headphones properly (meaning they don’t get loud enough).

There is no “minor purchase” that will make your audio better. You would have to spend several hundred dollars (at least) for a sound quality improvement that’s so imperceptible to the average listener that it’s probably just the placebo effect.

Having said that, if you fancy yourself a real audiophile and think you can tell the difference between 320 kbps and lossless audio, go nuts. Some people (maybe 1% of the population or less) might actually be sensitive to this type of stuff. But it won’t be cheap.