In the Version 1.07 Operating System update for the FR-8X V-accordion, a parameter called "Audio Boost" was added. This will boost the overall volume of the entire instrument.
You can use the following link to find information about how to check the current version of your accordion, and how to update if necessary:
Once your accordion is up to date with version 1.07, or ideally 2.00, you can use the audio boost parameter by following these instructions:
1) Press the menu button
2) Use the data/enter knob to scroll to the "system" page
3) Use the same knob to scroll to page 14.4, called Audio Settings
4) Press the data/enter knob to select and highlight the parameter "Audio Boost"
5) Turn the knob so that it says "on"