One driver for sale. You can use this to upgrade your MP20 to an MP40W. I think you will also need to buy a new power supply as the MP40 uses as 24V 2.5A one. Check the back of your MP20 one and see what it says. You can buy it directly from Ecotech or save some money and buy one like this from an electronics supplier:
http://www.rpelectronics.com/Default...5-24-P5-A3.asp
Price is $75.