A different look is that the rise time of the average signal in a digital transfer at the receiving end is 25 nano seconds. The signal travels down the wire about (roughly) 2 nano seconds per foot.
(now it could be done faster, but that creates problems, so the usual setup runs around 25 nanoseconds for the signal rise time)
So then you have the inevitable reflection, if it is an RCA, they just are not 75 ohms. (and the stuff in the receiving end mostly is not really a perfect 75 ohms, so you are going to have reflections travelling back up the wire, then bouncing back at the origin)
So the signal takes 25 nano to peak from zero, well if the wire is short, the bounce and back is going to mess with the system getting the correct reading of the initial pulse. and thus a problem with the signal getting messed up is added.
So if your wire is two meters, or six feet, then the bounce and back is 6 ft plus six ft times two nono per ft or 24 nonoseconds and the bounce back hits and the wave bump arrives back just at the moment you want.
Now this is a pretty lame condensation of various things I have read. But it is a good enough reason to buy a longer wire.
Right now i have a 26 ft wire because it has just by chance some so called 75 ohm RCA crimp on connectors, and I thought I would try it. It has less high frequency hash than a shorter cable.
I plan on buying a 13ft cable.
But i would go with a minimum of two meters if you want it shorter. but not under that.
Longer is not nearly as much of a problem as too short.
If the DAC has a faster rise time, the the wire could be shorter, but like I mentioned, too long does not seem to be nearly as much of a problem as too short.