GA-Z87X-OC vs. Maximus VI Hero

Many of the features are arguably similar.

Yes, the SUPREME-FX audio solution would be noticeably better. However, it depends on how good your speakers are. Crappy speakers will see little or no benefit. Great speakers will sound FAR better with the Asus solution.

I tested this myself between a comparable Realtek and addon sound card paired with M-Audio AV40's and trying to use the Realtek solution was painful to my ears due to the muffled bass and other differences.

I can't think of a solid reason to recommend the Gigabyte board aside from a small price difference, however buying a sound card would then make the Gigabyte solution more expensive (and take up a PCIe slot).

Since the SupremeFX is onboard this should also mean the FRONT AUDIO from the case works with headphones which doesn't work when you use a sound card.