Well, I might be late to this thread, but to talk about OP original statement, with moderns DACs, it's clearly impossible to distinguish them.
Let's be honest, people that justify that they can hear the difference do that to justify the money they spent on a ultra expensive DAC, or cable, or amplifier. As an electrical engineer, it's a pain to read a lot of misunderstood and false things on the Internet, about cable or DACs, or even amplifiers. I tried myself in blind tests to make the difference between two DACs, the one in my headphones amplifier and the one in my PC SoundBlaster soundcard. The one inside the amp is a PCM5102 with a DNR of 112 dB, and the one in my sound card is an ESS SABRE 32 with a DNR of 122 dB. Of course on the paper the ESS SABRE is better in terms of dynamic range and SNR, or even distorsion. But in real life, no one can make the difference between the two. I tried to distinguish them in blind and non blind tests, and the difference is non existent. They both have very good performance, and no matter what people will say, distinguish them, even in a non blind test, is impossible.
Then, we go about cables, the hardest myth around here. A cable is simply ideally a conductor, realistically it'll be a really tiny resistor with parallel capacitors and some inductances, but they are extremely tiny and small, and for audio applications, these are completely negligible. I wanted to test myself in blind tests, non blind tests, and even to test the cables with an oscilloscope and a signal generator. Prepare yourself for the result. I bought an AmazonBasics RCA to jack cable, 1.8 m long, and an audioquest RCA to jack, evergreen model, 1.5 m long. First, on blind tests, I was totally unable to make the difference between both of course. They are just cables with copper conductor, and except if the cable is really poorly designed, if the copper thickness is too small, on long distances you'll notice losses on signal intensity, but it'll not give the signal any color. Then, non blind tests, same thing, no difference at all. Concerning the build quality, the audioquest one is a little bit better, but the price difference is not a justification here because the AmazonBasics is excellent especially for its price. Here comes the interesting part, the frequency response I made using a signal generator and an oscilloscope. I expected the cables to have a frequency response up to some MHz, and I was right. I'm talking about -3dB response, and interestingly, the Amazon cable has a wider frequency response, from 0 Hz (continuous signal) to 50 Mhz, while the qudioquest one goes up to 30 MHz. Of course we don't care of such wide frequency responses for audio applications. But here you see, the amazon cable is fundamentally better, for a very much lower price, and with a bigger length. An important note, the frequency responses were totally flat for both cables, so NO color introduced at all. I finally returned the audioquest one and kept the amazon cable. I ended up by using only AmazonBasics cable for my installation because the build quality is excellent, especially for the price.
A more interesting thing to finish. People who think that cables which are used to transport digital signals change the sound. Of course we can all agree that an analog cable can pick up some interference and give them to the amplifier, but both cable tested before were excellent on that point. But then, for digital cables it's even worse. So I decided to buy two cables, an audioquest tower USB A to USB B to connect my DAC/amplifier, and an amazonBasics (again), 40€ for the audioquest, 6.50€ for the amazon one. I first tried to transfer some files to an external SSD, and both cables were topping at 50 MB/s, which is the physical limitation of good USB 2.0 implementation (theoretical is 60 MB/s). So thanks to my motherboard, and we first see that both cables are equals on that point. Then, sound tests ! I did a frequency response of the DAC/amplifier with both cables, and I noticed that nothing changed. This is not surprising, because we are transferring digital datas. That's all the advantage to transport digital data, picked up interference DO NOT impact the DATA at all, except if the interference are really powerful. I presume both cables are well shielded, and I couldn't test their frequency response as my signal generator didn't go above 100 MHz, and they were still giving the full signal without attenuation at 100 MHz. One thing interesting is that the audioquest cable is disconnecting from the PC if I move it a bit, which is disappointing on a such expensive cable. I ended up again returning it, and keeping the amazon one which is really good.
So what I'm saying here is, don't ruin yourself in cables, and keep that money for headphones/speakers, or better/more powerful amplifiers, because speakers are the elements of the chain that will give a color to the sound because of their characteristics, or because of the case in which they are, or even the room.
An end note about amplifiers. As i'm an electrical engineer, I know how to design amplifiers, and on the audiophile world, I see a lot of non-sense, I always end up to see amplifiers marketed as "pure class A with no feedback at all", and this is dumb as hell. These amplifiers are BAD amplifier, really! They are not stable at all, they consume a lot of power. Class A for headphones amp or preamp is ok, but NO FEEDBACK is a huge mistake, and those amplifier should be avoided by the consumer. Negative feedback MUST be used when designing amplifiers, and it DOES NOT affect frequency response, except if you're a bad engineer.
Thanks for reading and sorry for my English, i'm not native.
