I think you can use the voodoo mod (if you're rooted) to reduce the bottlenecks that Samsung place on the amplifier chip. Other than that, I'd recommend using a different music app with a 10 band EQ (Winamp for example).
And when you adjust the EQ, bear in mind the music you listen to. Classical won't sound better when you have the bass boosted, and most electronica will sound worse with prominent mids.