There are two ways, I explain one in the Tutorial.
In DVD2AVI, in Audio tab, just tick Normalize and that will lift the audio up to "Normal" level. Also under Audio/Doilby Digital/ DRC by selecting low medium or high will also increase sound level but will also distort it. I leave it off.
If you want the audio to be louder still, when encoding with TMPGEnc, select Settings/ Advanced / Audio effect and click the Normalize button. Enter, say, 150 or 200 and it will search through the Audio and make a suggested gain. Hit OK, ok and encode. It will blast you out of the room.
Making the settings to high as above can also induce clipping on load sections and induce distortion, so use wisely.
PS: Any feed back on M1-Edit?
Cheers,
CM