Right now the volume for all Dynamic Surroundings sounds is a lot higher than all other Minecraft sounds on my game and without going in and reducing the volume of every individual DSurround sound, it's deafening. Please could we have a global volume control for all sounds from the mod?

Which version of DS? There should be a global volume control option under Minecraft's sound option page.

EDIT: There should be 2 additional sound sliders. One for BIOME which controls the ambient sounds (background biome related sounds), and FOOTSTEP which controls, well footstep sounds. Other sounds are controlled by the other sliders, like ambient and weather.