Why does USB feature so much in discussions about DACs when the newer HDMI seems better?

@vthokie83 

No worries!  When I started this thread, I was mystified why USB was so prevalent when there is a purpose designed, point-to-point solution for high-bandwidth multi-channel audio in the form of HDMI, which is ubiquitous in modern TVs and Audio Visual gear.  I never expected anybody to mention 'legacy' formats like SPDIF or Toslink  and I had never even heard of I2S.  It seems that the inventor of extending I2S over cable is only interested in 2-channel audio.

I remember the fuss that arose over the introduction of 2-channel stereo when mono had been the only option.  It was going to practically double the cost of HiFi for goodness sake.  Now I am wondering if there is a similar reluctance to move to multi-channel audio, for a similar reason.  Multi-channel high-definition audio has been available on SACD for over 25 years now.

For what it is worth, I have an 8.1 system with no center channel.  The main front speakers are better quality than the rest!  Generally, the rear speakers carry ambient sounds from SACD but some recordings on Blu-ray have Atmos and use all my speakers for truly immersive sound.

Oh, that recommendation to keep HDMI cables short only applies when they are not carrying native HDMI signals!

@richardbrand 

You're a total knob jockey, go back to ASR

Many historically early electronics included USB because it was cheap. Unfortunately many audiophiles got hooked and believe mistakingly that it is a good  way to connect a DAC. It is not. I2S came along in quality devices and before that HDMI. Both are superior for audio. But for those who disagree… fine. You use the connection you like or have. Many people use computers for their source and connection through USB to their audio system. I don’t knock anyone’s setup. If it sounds fine…. there isn’t something to fix.

I am not disagreeing that HDMI might be superior in some ways, but I think the answer is that USB works. And from an engineering and cost standpoint it would be difficult to make the case for using HDMI. More wires does not mean better, USB is more than capable of providing the bandwidth for hi-res audio. 
 

As others have stated, HDMI connections have been popping up on DAC’s to accommodate I2S, not because it is inherently supported by the HDMI standard, but because I2S requires more wires to pass the signal. 
 

I will step out on a technical limb here, so please feel free to correct me, but USB audio uses a packet protocol similar to most digital communications systems. Whereas I2S is a low level hardware signaling protocol meant to be used on short buses between hardware components. Is it better? Very possible, but it is totally up to the implementation, which for now has no standard, and may be prone to corruption if not done well. USB, by virtue of using a packet protocol has some verification capabilities to ensure accurate data transmission, I don’t know, but I am guessing the I2S signaling does not have this capability. 
 

Back to the answer, they use USB because it works and makes technical and economic sense. Again, not disagreeing that I2S might sound better under the right circumstances, but if you ran the same packetized protocol on HDMI that you run on USB, there would be no inherent advantage, and it would be overkill.