If the caps you want to replace are not leaking or malfunctioning, one idea is to bypass them with a very small value, like a .01 uf, high quality cap. Bypass just means solder new cap leads to old cap leads, just in case you have not done this before. You don't need to know the values of your existing caps to do this, and it should be a good improvement. Madisound has a good selection of poly caps that will work if you choose this route. If not, you need to buy a meter from Radio Shack, desolder, and measure your caps to get the values.