Increasing the ChannelTxGain number makes the audio coming in via the IBI202 louder in my ear.
Increasing ChannelRxGain makes my microphone audio louder in the other person's ear.
The changes seem more limited than the 24 db (12 dB-(-12 dB)) range would suggest, but sound levels are hard to judge. The increase to 12 dB for ChannelRxGain has improved reports for the audio heard by the other end.
The original settings are each 0 (zero). One dB is about the smallest amount that one can perceive. Ten dB is perceived as about twice as loud, and -10 would sound about half as loud.