Yeah, what Ed said.
All I can provide you are guesses. R9, R13, R anything - doesn't have a universal meaning. They only have a meaning when you pair the amp with the appropriate schematic. I don't have one for a Coliseum 300. If you do, post it. In fact, you could post pictures of what the damage looks like.
A loud hum is almost always an indication of something wrong in the power supply, be it shorted or open caps, rectifier or transformer. The pop could have come from a cap - if they get leaky and pass a lot of current the electrolyte can actually boil inside of the cap. When electrolytics boil, you will get some crackling, as will happen when resistors burn.
Until you know what is actually wrong, you don't know what it will take to fix it. But I'll tell you one thing, parts costs are going to be nothing compared to the labor.
