Welcome to Talkbass!
Can you clarify, please, is your tone "muddy" when you are practicing home alone, or is it muddy when you are playing in a band with other musicians (or both)?
How is your "muting" (aka "dampening") technique? Or in other words, are you taking proper steps to stop the unplayed strings from ringing out?
Poor muting technique is the most common cause of a "muddy" sound for beginner to intermediate players, in my experience.
If you are looking for equipment tips, the best advice I can give is, don't be afraid to use that EQ! Try changing your settings from "flat" and see if you can find a setting that is less muddy.
I am also curious if bypassing the Boss CS3 and Sansamp, and plugging your bass straight into the Ashdown, improves the sound at all?