How can I stop a desk from vibrating when I type?
Is the ledge that the monitors are sitting on actually attached to the desk? It kind of looks like it's just resting on the speakers (Btw, I swear I had those same speakers like 15 years ago). Since there is some natural bounce in any kind of wooden surface like you have, my guess is it's transferring to the upper support which will naturally be prone to movement due to not being attached. If you add at least 3 supports so it can stay up on its own (not relying on speakers) I would guess most of the movement will go away.