Depends on your source component and DAC. I can't do coax from my old MacBook Pro to my NAD M51 DAC, but my LifaTec glass optical cable sounds better than USB.
I've tried them all. On my setup they all sound amazing and as of now I use all three ...NAD DAC to McIntosh MA 252 uses balanced cables. Tv to DAC uses optical. Transport to DAC coax.
Assembled my own digital coax cables using tips from the Max rochlin memorial website Max Rochlin Memorial Digital and Video Signal Cable. DIY Audio Kits Reviews The tips about cleaning the cable with deoxit to release any contamination and follow with a solvent like meths or white spirit to wash it away (tip from deoxit website to get the best connection), before soldering really make a difference imho. Some think that overkill but if you're only doing it once making your own why not. What I've heard about optical is the cutting of the fibre makes a huge difference in that it needs to be a clean precise possibly polished termination, so best get a quality one.
Back in my days of helping friends & neighbors setup their home theater systems back when Best Buy was selling everyone on optical cabling, I can't even remember how many times I got called over to help fix an audio issue, only to find out that the optical cable was being treated like any other cable when routing it behind the TV/audio stand. Those cables do not like being flexed at all. I always use coax just because of this.
Sorry I was on my phone at work. It uses an xlr cable to transfer the digital signal. I've tried optical and rca and I prefer the sound of the xlr digital cable (abs/ebu).
The short answer is “coax”. if you aren’t listening to resolution higher than Red book cd, you won’t hear a difference. If you are paying for hi-res, you aren’t getting it with optical.
I had thought that issue existed—Toslink !192—but I can set my iMac to 192 and there's no issue at all via optical to Fluance Ai60 powered speakers. I had previously noticed that issue with other powered speakers (Kanto TUK), but it turned out to be a limitation of the speakers, not the optical. The Kantos support only up to 96 via optical. "Still sounds great" is the most important thing, anyway.
I have an old (2009) Dell laptop that has a kind of "hidden" coax. The PC has to be set to use it—you first need to discover that capability—and a dongle is required. I used that config for a while outputting to a Cambridge Audio receiver. It sounded just fine, although really, not any better or worse that going from a Macbook Pro via optical to that same receiver.
With red book CD, varying from 16 to 24 bit, I never heard any difference between coax and optical. Didn't matter whether it was a 1k or 30k costing stereo system. When playing Hi Res recordings I noticed that coax and USB sound better, at least in my system.
I'm getting 192/24 just fine with optical using a WiiM Mini to a Marantz SA-KI Ruby. So no problems at all here with a run of the mill 3 meter optical cable. So I'm not sure how one can say you can't get hi-res with optical. I was just listening a Bill Evans album from Qobuz in 192/24. Sounds great! I've had more issues with tight fitting RCA connectors on female RCA connectors that weren't robust enough. I've had several components with female RCA connectors come free and become unusable. I've never had an optical connection or cable fail in the many years of using them.
SPDIF = 75 ohm coaxial... back when first introduced some fiber connections were improved by using optical gels to minimize light scattering at the interface.. AES/EBU xlr = 110 ohm cable..
What I find contentious is when someone posts incorrect information. That being one can not get hi-res when using optical. If those that posted that they are getting hi-res with optical didn't post their thoughts some might think it wasn't possible due to misinformation posted by some.
Misinformation runs high in the audio world. Passing on bs like the women passing on gossip at the bingo night.
The long held belief in coax being superior to optical was no doubt a worthy one 20 years ago. The implementation of the technology advanced over time and leveled the playing field. Reminds me of the years of jitter angst, which has been a solved problem for quite some time. An example .. @Archimago did a very comprehensive review on the SMSL DO100 DAC which sells for about $250 and his measurements show incredible jitter performance on each input (coax, Toslink, and USB). He measures 16 and 24 bit, 44.1 - 192 kHz (yes, Toslink at 24/192). It's a good read. IMO choose which sounds better to you or is perhaps more convenient and don't give it another thought.
For cd like the 6000CDT either is fine, since hi res access is not applicable. For streaming I prefer coax. I’ve had spotty access of 24/192 with optical, although fine for anything less.
Toslink is S/PDIF over optical. The standard says POF (Plastic Optical Fiber) but a glass fiber can do the job as well or maybe a bit better as in the past the attenuation of POF was higher than in glass. Modern POF has a very low attenuation. In the past Toslink struggles as the LED's used to power it were a bit slow. This was also the reason for a higher input jitter compared with coax. Modern Toslink (the 3 Volt) performs much better. The standard says 2 channel 24 bit 96 kHz S/PDIF is de max. OS like Windows or OSX gap Toslink at 96 kHz. If you bypass this e.g. using WASAPI/Exclusive you can often go as high as 24/192 depending on the modules used in both sender and receiver. In a unsighted test, I'm not able to tell them apart.