Comment by zer00eyz

https://www.youtube.com/watch?v=wqAsOxUrXIw at about the 54 second mark you can see how this system does size sorting of trash (legos are not trash)

A combination of pins and holes will get you roughly sized items.

A vibrating table with lots of W snapped channels underneath is going to help too.

A belt with "scoops" is a great way to feed out of your initial hopper, if you drop it onto a perpendicular belt (one with W grooves) your going to get a good initial separation more naturally.

Air knives and puffers are your friend as well. Since you already have a detection system running it twice might be of benefit to you, just puff off anything that you can't sort as a single item.

I don't think "quite" and "lego" really go together so no happy solution for you there other than sound isolation.