You didn't post a schematic but I have repaired a number of these types of biamped monitors. Generally the first cap that is going to fail and cause a huge buzz is the main power supply filter cap which is the biggest cap in the mess, usually a 4700uf, maybe as low as half that. These caps are usually mounted on a double sided board and buried in glue. You can cause a lot of intermitancies if you don't properly work the double sided boards using the cap leads as feedthroughs. I generally double the voltage rating of the caps if they wil fit.