if you dont have subwoofers, then programs like 'enhancer' can help because they can artificially add the lower sounds, but if you arent getting your highs like you want then you should look into better speakers and amps... and if youre going to do that, you might as well add a sub too.
Jeeze. I should have expected enforcer to have a reference .
Personal experience, when I compare a flac file to an mp3 on my mid to high end system it is night and day. Crisper highs and much cleaner bass. That's just me though.