Yes, 20706 seems no mclk output , we usually to test with two ways:
1. add an external mclk
2. choose a codec which do not need the mclk .
if you can upload the spec of the codec, we can help the check.
I known this two way & tested.
1. Did you know which parts can do external mclk & synchronized with I2S SCK / WS?
2. The codec is integrate solution with amplifier, we must to use it, so no other choice.