I agree it will be a tricky one to make sound really good, but it shouldn't be difficult to restore functionality. Since audio amps are pretty popular, you have a whole slew of project options floating around, and there are some complete kits or PCB/instruction kits available that could be a good starting point for understanding how they work and then maybe making modifications.
If one of your tools is an oscilloscope (or even a multimeter that will read AC voltage to at least some tens of kHz) you may be able to find some noise on power rails or something that's giving you the static, it could be a gradual capacitor failure or similar if the unit otherwise seems to be working. Potentially fixable if you can diagnose what part is the issue.