well if i ever sell my amp i got offered a treo 750.1, an ia 20.1 and a concept 2400 that will be in my price range which of these will be the most efficient and give me more output than my md2d
i owned a 20.1 before. they are pretty nice amps. it will give you more power than the m2d2 and they are built real well.
but i dont know if you will notice a huge improvement over the amp you have now. i found that it was a nice amp, but unless you plan on wiring below 1 ohm, you really dont get to see all the benefits of owning one.