I use the USB to playback mp3s on a 6 speaker professional head unit stereo. The stereo isn't the best and some tracks play far too quiet.
My solution was to use
http://www.howtogeek.com/howto/20700/how-to-adjust-the-volume-of-your-mp3-files/
This MP3 gain freebie worked a treat I set the dB to 98 imported a file of 100 ish tunes. To get this dB increase a lot of mp3's were 'clipped' by the software. This isn't ideal. It has put my amp processor upgrade on hold it's worked that well . I will be adding tweeters to my system but that's all for now. A great free volume gain.
My solution was to use
http://www.howtogeek.com/howto/20700/how-to-adjust-the-volume-of-your-mp3-files/
This MP3 gain freebie worked a treat I set the dB to 98 imported a file of 100 ish tunes. To get this dB increase a lot of mp3's were 'clipped' by the software. This isn't ideal. It has put my amp processor upgrade on hold it's worked that well . I will be adding tweeters to my system but that's all for now. A great free volume gain.