Can you adjust the volume of the Max Trainer's console's sound effects?

Yes.

M3 model: First, push and hold down the Burn Rate/Increase and PAUSE/END buttons for 3 seconds while in the Power-Up Mode. The Console display shows the Sound Settings prompt with the current setting. Push the Burn Rate/Increase or Burn Rate/Decrease buttons to change between the settings of "OFF" and "1" through "7". A setting of "7" is the loudest volume. Push START/ENTER to set.

M6 and M8 models: Simply adjust the volume by pressing the VOLUME button on the console. It will cycle through the options of: off, low, medium, and high.