I know somewhere on the unit I stumbled accross a volume setting and I got warnings about if I set it over such and such I could damage my ears.
May be your still set on the "safer" side and thats cutting the DB in the base?
I once made a lil amp for my Ipod, Im thinking it would be the same for the phone, here is my instructable on it:
5.00 Ipod Amplifier
Cheap and mighty 5.00 unit.