Compressionless brake outer, new inner cable, plenty of cable lubricant. Avid SD levers are the best match for cable disc brakes, and once you have the right components, it's a matter of setting them up properly. Run the fixed pad as close to the rotor as possible without major rubbing (although it may brush occasionally, that's ok), then bring the moving pad in by pulling cable through, and set it in position depending on how you want your lever to feel. Also play with reach adjustment of the lever, and if you get SD levers, play with the dial to get the power/modulation you want.
They aren't bad brakes, I ran one for a while and was happy with its performance, they just take a bit of tinkering to get right.
Another thing I shouldn't forget to mention, is maybe the pads+rotor need a clean, so hit them with a bit of medium grit (400 maybe?) sandpaper, to take off any glaze they may have.
