We want to generate 8.200 MHz as I2S MCK with an nRF5340.
This could be achieved with 12.300 MHz ACLK as source for MCK, and then dividing by 1.5 in the Master clock generator.
An MCKFREQ register value of 0xAAAAA000 = 2863308800 looks like it could do this - BUT with the formula
given here, the denominator 
is always an integer number, so it can only divide by 1, 2, 3, 4, ... but not by 1.5 (as we would like) or any other fractional value.
Is this true? Can the Master clock generator only do integer ratios despite its MCKFREQ configuration register suggesting many more possibilities and fractional division?
If so, we'd need a separate external oscillator just for this frequency - or another good idea how to generate it with the nRF5340.
