Most of the time, optical loses out. It often suffers the most jitter of all connection types, plus it has the lowest bit rate/resolution limits, so that comes as little surprise that it rarely ever comes out on top compared to coax, unless you have a major issue with the coax cable picking up noise (which optical won’t).
U18 came in today and I was able to get I2S working without too much effort. Toggling through all four settings on the U18 didn’t work with the default setting on the Draco. When I left U18 in Gustard I2S mode, and then started adjusting the I2S mode on the Draco, the first option I changed it to (from default) worked perfectly for PCM. Did not yet get a chance to test DSD, but I typically won’t be using my Musician Draco for DSD anyway (I have a Cayin RU7 1-bit native DAC for that material anyway).
Coax can be better than optical and vice versa. For me Supernova 7 optical beat regular amazon optical. Aliexpress Odin 2 Coax beat amazon optical. Supernova 7 optical beat odin 2 Coax. Audio Envy and Atlas Ascent Ultra Coax beat those.
This essentially goes back to my comment about coax and noise rejection. The better coax cables will do a better job rejecting noise. The science leads to the proof (your experience with different coax cables). I am not sure why different optical cables would perform differently though, at least not clear on the science behind it (not denying it to be true, just don’t know the reason behind it). Certainly an interesting subject matter, but as we all know, cables are an eternally hot topic in general in our common hobby here.
Audiophile optical can make a large difference in a revealing system for sure just like the rest of cables. Thankfully I'm not stuck with optical though. I think optical is on all devices because it breaks up ground loops and doesn't pass high frequency noise, good in those scenarios. If your system isn't noise mitigated enough this is probably the correct choice to avoid fatigue technically speaking. I love how relaxing optical is in those scenarios, it's a real improvement if it's bad enough noise going on. Optical does still pass the degraded SQ in the system from noise in general and will improve as noise is removed from the system. Jitter is the worst though so it would hard to make it the ultimate choice for a cable. I2s is the best at the time IMO as it bypasses things and goes straight into the DAC, it's quite audible. A good coax or AES does the trick for me though thankfully. Some high end DACs bypass the issues of jitter and noise by internally bypassing clocking and you won't hear near as much of a difference between any of the inputs then.
I like the idea that optical completely isolates electical noises from source, but didn't realize that the conversions of light/electic on both sides could introduce jitters.
The BNC cable I use is an Audio Sensibility's Statement, which uses a silver conductor with 4 layer shielding. I don't have many experiences about digital cables and guess it should be fine for my system.
