Use Debian's gnome-alsamixer, alsamixer, or any other ALSA mixer program (needn't be from Debian, but AFAIK one doesn't exist for Maemo) to adjust the DMA control up maybe 4 notches. Easier options (depending on what you're trying to play, and how you're playing it) might include losslessly amping your mp3s with mp3gain or configuring mplayer with softvolume, but the DMA tweak works for all sounds.