Since they mention DBT, I put it here vs. PC audio forum.
It is only nit-picking, but some of the sample rate limitations listed (like the Xonar STX not supporting 88.2 and 176.4 kHz) are actually due to the Windows drivers, rather than the hardware itself.
Also, volume matching could have been done more accurately by measuring the output voltage, rather than acoustic levels. The measurements do suggest possibly high output impedance (increased bass level) for the ALC889, so that could very well have been audible even with relatively high impedance headphones.
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On topic, it's an interesting article. There are some methodology issues that have been mentioned on r/headphones, but it's an interesting read nonetheless.
Well, that can be easily found out because the noise should be audible even while no music (or a silent WAV file instead) is playing. If it is not under any system activity, one might just as well save the money. Although both the Realtek and the Xonar might have output impedance issues with low impedance headphones and IEMs, which the large majority of consumer models are to be compatible with battery powered portable devices. On the other hand, the Xonar should normally be well shielded from computer interference, when it does happen, it is most commonly because of a ground loop with a grounded external amplifier.