I'm not an audiophile but I do know something about motherboards.
First, most of them seem to have a Realtek sound circuit so there's no big difference to be expected.
Second, the quality of motherboard components has improved vastly in the last decade or maybe even two. Supposedly the sad example of a few reputable manufacturers going down due to failing capacitors made the rest stop cutting their expenses in the wrong place.
Third, there's motherboards that try to improve the built-in sound quality. Some have invested in another sound circuitry like SoundBlaster, some have improved the shielding etc. You'll notice if the manufacturer has done something extra to improve the sound, they tend to advertise it on their product sites.
Fourth, if you're interested in getting a motherboard with better audio, try to find a comparison review for the models you're interested in.
Fifth, although even the cheaper manufacturers have improved their build quality, I'd rather trust the premium names. Their availability and service is good and their pricing isn't any higher than that of the less known brands.