So what do you want us to calculate exactly?
... just... calculate something that is pretty easy to calculate, instead of always hand-waving. Like, I really and actually calculate series resistor for LED current limiting, instead of always slapping 470 ohms. Isn't this normal? Why is this a bad thing?
I mean, we can babble "no need to length match I2S" until cows come home, but how close of not needing it we actually are? By doing a simple calculation, we can put these adjectives to numbers. It's called engineering.
Example calculation:
I2S clock = 12.288MHz -> period = 80ns
Allow for 5% drift from optimal middle point sampling -> 4ns
Speed of electric signal in copper = 200M m/s
200M m/s * 4ns = 800 millimeters
Look, it took less time than writing a handwaving reply. If you never calculate this, how do you know how close or far you are?