I'm studying electrical engineering myself , and I never thought of trying to modify digital units at home.
If you have a problem within the unit (some resistors , diodes , etc. are open or not functioning) , open the unit & check these out with a Multimeter , use identical components to repair damaged ones.
Actualy poor sounds may be a result of Bad components (cheap units uses cheap components) , or Bad circuit designing (cheap units may not have the best circuit design for a given effect).
