ac3filter > ac3filter config > main > preset > loud

and

ac3filter > ac3filter config > mixer > gains > master > value (let try a big no. let say 20 or more)

This is the best method to do so. Only u may feel the sound volume being decreased after some time because it is for auto gain to stabilize. U can change the master value again until u find a value that fits to the movie even after it drops the volume.

If still not satisfied, u can also try the extreme way.

mixer > gains master > uncheck auto gain control

and / or (depends on the movie u played and your system)

main > gains > uncheck normalize

but it may affect the sound quality and cause unexpected loud volume, so using them as last way.