List of available upgrades:
AR Cone- Stronger/reinforced cone/surround
Direct Leads- 8ga wire applied directly to the lead wire instead of soldered to the push terminals
Black Carbon Fiber Dustcap
Red or Blue and Black Carbon Kevlar Dustcap- Both options obviously have cosmetic value but also add strength to the cone.
Level 4 upgrade for Level 3 subs- Level 4 coil and 1 extra spider if necessary.
Xl upgrade for Level 4 Subs- XL coil and 1 extra spider if necessary.
I think thats all of them.