Glad to hear you're really into sounds...and LOUD too!
Well, Milton clearly explained the logic involved for all the Avia aircraft series.
The truth is the designer went to great lengths to reduce interior sound levels - even the specially inlaid wooden floors were for sound reduction as much as deco.
The most practical way of hearing louder sounds is obviously to use your computer audio master contol.
Normal settings should be about 50% on all sliders. Even this is too loud for my setup (30%volume is almost deafening for the '56).
Don't be afraid to play around with the settings according to what you're flying.
Are you taking the sounds directly from computer to headphone?
Or are you using desktop speakers with a headphone jack?
Makes the world of difference.
I'm afraid to make the whole soundset louder, this would mean a combo of revised cfg file and amplification of wav files together...that's a fair few weekends Lol.