The Avid disc brakes I've seen were either BB5's or BB7's (unless you have Elixir hydraulic discs). The BB7's have an adjustment on the non-moving side that the BB5's don't, so you can better tweak the adjustment on them. Avid Speed Dials are good levers to use with either. You'll adjust the Speed Dial levers for the longest pull, using them with disc brakes.
 
I've seen Avid Single Digit 7 v-brakes, but never Single Digit 7 levers or disc brakes. Where are you reading the Single Digit 7?  
 
Edit: The RANS page on the Seavo says BB7 disc brakes and "Avid Digit 7 Aux". Does it have both a disc and v-brake on the rear wheel, like the photo suggests?

Ah, I've never seen a rim drag brake before.
 
The key with adjusting BB7 disc brakes is getting the non-moving side adjusted. Pull the brake lever while watching the disc brake and see which side moves. Now, go to the other side and adjust it in until it starts rubbing the rotor, then back it off just enough to clear. If that non-moving side has too much clearance, it's hard to get good brakes without having the other side rub all the time. That's what makes BB5's so hard to adjust (and makes them not worth buying, IMO), the fact that there is no adjustment on the non-moving side.