Are you talking about component systems, or subs? If components, the d971(2-3 year old model) and the hexpro are essentially the same, the hexpro uses a soft dome tweet, the d971- metal dome. The woofers appear the same, at least it's the same motor/basket, and the xovers are the same except for color. TDX I believe is just the name for their heat dissipation technology