Min & Max power, in grayscale mode, are used for the white parts and black parts of the image, respectively, and everything in between those two brightness values will fall somewhere in between.
Going slower or faster will darken or lighten the image, because you’re putting more or less power down on the material in a given period of time. Using a higher DPI can help too - too large and you’ll get gaps between scanning rows, and your LED should be able to give pretty good detail. Make sure it’s properly focused, as that’s pretty important.
Your other settings are reasonable, but check the $30 setting in your firmware (type $$ in the console and look at what it spits back out). Your S-value max is set to 255, and should match whatever the controller is set to - if it’s 255 you’re good, but if it’s 1000 (a common default) you should set the S-value max to match it, and that would help too.
Check that and post back.