Is there a way to adjust levels of audio inputs on an AV receiver?

Richard has an Oknyo TXNR906 AV receiver and one of the HDMI inputs are lower than the others by 3-6db. Scott says that he's never heard of that before, although 3db difference wouldn't be as noticeable as a 6db difference. There could be an audio adjustment feature for each of the inputs in the setup menu. It may be possible to change the output of the devices going into the receiver to bring the levels up.

He's also vision impaired and Scott recommends Dancing Dots for blind and low vision performers.