Im not sound expert but integrated Realtek HDs killed majority of external sound cards.. so probably their sound capabilities are good enough
Frankly, integrated audio isn't the only thing that "killed" the sound card industry. Creative trying to strong-arm/weasel everyone else out of the market didn't help, then they sat around trying to over-charge for mediocre hardware without innovating. Given that on-board audio was becoming ubiquitous, why would people bother paying Creative prices for hardware that never delivers on its promises?
Nonetheless, I wouldn't necessarily say that the sound capabilities are "good enough". My old UltraSound still produces more pleasant sound than a number of the on-board audio implementations I have. I have never encountered one that didn't have some level of noise in the signal or audibly poor frequency response. It really depends on the manufacturer doing a decent job on the audio section, and they (somewhat justifiably) tend to focus on other aspects of the motherboard.
In that respect, I am in full agreement with Tiido. For real DOS, quality hardware is always the way to go. While emulation and TSRs tend to work sometimes, they are never my preferred solution, so I will read any development/progress reports for such projects with great interest, even though I can't always afford the end product.