+6 dB... sounds like an iPod to me.
Anyway, I set my precut to 0.0 dB; this was to compensate for the headphones I have (a set of Magnavox MHL1600 headphones), which have pretty powerful output. I can lower the volume down to -23 dB on my iPod and it's still pretty loud.
If your music sounds way to quiet, then try raising the precut.