Hi Kijanki, I agree with everything you said except for this one thing: "...jitter does not even apply here".
Just because the source clock isn't used inside the DAC doesn't mean that it has no effect. The DAC clocks data only after it reaches the DAC. The source clocks data up to that point. Source clock jitter combined with cable jitter may err a bit before it reaches the DAC.
For short cable runs, bit errors induced by the cable are unlikely. For long cable runs, bit errors are inevitable. Therefore, the longer the cable and more marginal the source, the more the cable matters for both function and SQ.
Of course, as you mention, a cable may also help SQ by isolating the signal from various noises.
Just because the source clock isn't used inside the DAC doesn't mean that it has no effect. The DAC clocks data only after it reaches the DAC. The source clocks data up to that point. Source clock jitter combined with cable jitter may err a bit before it reaches the DAC.
For short cable runs, bit errors induced by the cable are unlikely. For long cable runs, bit errors are inevitable. Therefore, the longer the cable and more marginal the source, the more the cable matters for both function and SQ.
Of course, as you mention, a cable may also help SQ by isolating the signal from various noises.