Asus Xonar DX sound card from 2008 vs. Asus onboard sound from 2016 and HDMI

Those certainly look like electrolytic caps, although it's not clear if they're paralleling two per channel (to get enough capacity within the height restrictions) or using them for completely unrelated purposes like supply bypassing. More puzzling is why they seem to be quite far from the audio connectors, not that it would have much effect on quality.

For the most part, the analog output performance really only matters for those using headphones or old but still decent pro audio gear.

They appear to be Nichicon Gold capacitors. Not the worst you can get, and better than the vast majority of motherboard audio caps.

NiHaoMike said:

...the analog output performance really only matters for those using headphones or old but still decent pro audio gear.

Click to expand...

Yes, that is the topic, really the only topic...

Things have changed for the better, as you both now acknowledge. The question remains, by how much.

For analog output I would bet $5 of my own money on the Xonar putting out better sound. It's a discrete PCB, which adds isolation from the mobo, and its sole purpose was audio quality. Motherboard audio circuits are there because they have to be, and designed accordingly. They may toss a small bone with the Nichicon caps, but the "isolation" is mostly theoretical. A discrete (properly designed) board offers isolation.
For the record, just because caps are Japanese doesn't mean they sound good. They only specify that because Chinese caps are generally junk and they want to distance their product from that perception. If you want to go all out on audio caps, replace the ones (in the signal path) with something from Mundorf, Jantzen, or Solen.