The description of the options are on their website in which I've listed below. I imagine, like myself, you are wanting clarity on what they mean. I'm interested in Level 4's myself. Seems like the Level 3's would have me wanting more power.
Options
8ga Direct Leads- This upgrade adds 18" of 8ga OFC wire for your leads instead of using the stock push terminals
AR Cone- This upgrade adds the AR Cone/Surround to your sub. The cone is a kevlar impregnated reinforced cone with our large wide roll surround.
Carbon Fiber Dustcap- This upgrade adds our Carbon Fiber Dustcap to your subwoofer.
XL Upgrade- This upgrade adds the XL coil and our dual leaded spider to your Level 4 subwoofer.