There are such thing as mighty composite bows which you can add more str accordingly. Also yes there are ways to get more damage from bows, and it is something many archers forget about or don't like investing in and it is done by enhancing ammunition. The +1-+5 damage does not stack or the to hit, but its with other things like explosion or what nots. Also do not forget firing more arrows, just ignoring DR, or getting sneak/sudden/skirmish dice to each shot that requires an attack roll is a nice way to get extra umph. There are also things like targeteer fighter where you can apply some of your dex mod to damage, dead eye which gets your dex mod bonus to damage, and other things to get any extra damage.