Which version of volume+ did you try?i couldnt get the free one to work from the google play store on my nexus(unrooted using 4.1) so i signed up to the dev forums and downloaded the one from there and it works great.dont forget you need to enable volume+ in two places.in the program settings and in the phones sound setting.
Android Audio Hacks
edit-also play around with the settings.i noticed if you put the bass boost to high you will lose volume.also the one from his site has 20 volume increase settings and the ones at least for me that work the best is 10 and 20