It’s an apples to oranges comparison because the SPDIF connection goes through the U18 that may be providing a better clock, galvanic isolation, etc. Also may obviously be affected by differences in quality between your SPDIF and USB cables. The R26 is a good DAC and the Gugnir may just be a sideways move and think you’d need to go to a Yggy to get a meaningful improvement, but at that level you might also consider the Denafrips Pontus 15th as well. If I was you I’d try this HDMI cable — I use this between my DDC and DAC BTW to good effect — for about 7 bucks (for a 1 foot cable which is what you want to keep the i2S connection as short as possible, which is important) and see if the i2S connection makes a noticeable improvement, and if it does you might consider getting a better HDMI cable from DH Labs, etc. at some point. Just some thoughts FWIW.
Does your DAC sound better through the S/PDIF or I2S inputs than through USB?
For a long time I used a Windows NUC driving my DAC through USB. (A modified Gustard X20Pro.) Then I got an Aurender N100 which provided a better USB source. I also tried a DAC on the recommendation of a friend in the New Jersey Audiophile Society. People were excited about this there: the Gustard R26.
I found that the R26 is disappointing through its USB input, but excels through the Coax S/PDIF input using a Gustard U18 Digital/Digital Convertor.
This probably points to a subpar USB implementation, to be honest, but I started wondering if this is a general pattern among DACs that can take both S/PDIF and USB.
Anyone find something similar in their DAC?
For example, I'm interested in a Schiit DAC (not sure which model yet). Now that I have the DDC I can drive it through Coax and compare to USB. With the Gungnir 2, I may not have the choice of USB because they have a USB C connection and my only good USB cable is A to B.
Note: what is wrong with the R26 through the USB input: very light bass, unintegrated treble (sibilance kind of clouds over the sound and doesn't integrate with the body of the instruments)