I have DM10 connected via USB to my laptop. I have a Behringer U-CONTROL UCA222 connected USB to the laptop as well to send audio out to our band mixer, but I can also record the drums. Install the ASIO4All audio driver.
http://www.asio4all.com/Open a new Reaper file. Insert a new Virtual Instrument track and select Addictive Drums.
Under the Maximize\Minimize\Close in the upper right hand of Reaper, click the audio driver words (shoudl say something lke 44.1Hz 34bit Direct WAV..blah) or something like that. This will open the preferences(or go to Options..Preferences on the menu in Reaper to get there). On the left side of Preferences, under Audio, select Device. On the right side, select ASIOfor the Audio System and under ASIO Driver, select your USB Focusrite. Hit Apply.
You should see activity if you hit a pad. If your focusright is attached to an amp(or headphones) you should hear something.
Once that is done and you have activity and sound, we can talk about splitting the tracks up and all that other stuff. You have to have sound first.
DM10-->Laptop
Laptop-->Focusrite
AISO Driver installed
Reaper Preferences(AUDIO) select ASIO and Focusrite
Let me know if this helps.