@z3DD3r 's way of fixing it is way more elegant than mine, for starter the way I tried to "fix" it didn't even work on hammerhead(didn't know it could work for other device either). At least from what I've understood from the logs he configures the I2S/PCM interface inside the firmware configuration (hw_config_start && hw_config_cback) which means that changes are only being made inside the libbt-vendor module. Another thing is that with his fix all I2S/PCM related VSCs are being send to the controller, unlike the one used for hlte which sends only one (HCI_VSC_WRITE_I2SPCM_INTERFACE_PARAM).
The commit should be uploaded these days, according to what he said.