A simple test to determine whether its doing the job is to try 2 different coax cables, a cheap one and a good one and see if there is any sonic difference. If there is, then the DAC will benefit from lower jitter S/PDIF signal.
You could also compare 2 sources, like a Sonos, Transport, computer etc..
Most DACs fail this test.
Good point. This is a very fair and reasonable reply. Note that at the time I A/B'd my Yggy to Oppo UDP205, I also A/B'd it against my Emotiva ERC-3, which is connected via AES/EBU (and not coax like the Oppo). The improvement I found with the Yggy was the same vs both the Oppo and Emotiva. In fact the Oppo and Emotiva have the same "tinny" treble, one dimension and less authentic sound in comparison to the Yggy. Point is, the difference wasn't just because of one input type like S/PDIF. I hear improvement in the USB input as well, relative to the USB input of my M6si amp.
So I am using multiple sources.
I remain open minded to better cabling, but this isn't something I feel a need to investigate further at this time. I have (as do others) a degree of confidence that any cable supplied by blue jeans is going to be "more than good enough". Maybe not the best, but certainly good enough. Given the responses on this forum it wouldn't matter what cabling I purchased or how much it costs because someone will always point to something "better". Ditto for any other piece of equipment.