I am posting for the first time, and hope I am not teaching anyone to suck eggs, but the solution to this problem that I use is to increase the volume level of the song as you can't change the settings on the Ipod. Do this:
Open Itunes, don't connect your Ipod.
Highlight the song(s)you want louder
Open File on the toolbar
Select Get Info
Select Options
Move the volume adjustment slider, it's normally set to 50%, to a higher level. Experiment till you get the level you need.
Click OK
Connect and Sync your Ipod.
This works for me and if you need it any louder after doing this you should get a hearing check.