Tenor AX volume low

I am using the ax for calling cards.
When users call into the AX the IRV sounds loud and clear, however the voice coming from the destination is coming back low.

My question, is there a way to adjust the volume so the IRV volume does not change but the receiving voice (the called party) can be increased?

My setting are:
CAS signaling group-phone
Rx gain -6 dB
Tx gain 0 dB

IP routing groups
Rx gain 0 dB
Tx gain 0 dB

Thanks.