Good heavenswhat in the world did you do to your knees? I hope you weren't doing something really stupid, like trying to play touch football with your big brothers or the guys at work.
Anyway, I bet you're an advocate of hiking poles. They really can help you take a lot of impact away from your legs and knees. Plus, they're just great all-around for helping with balance and maintaining a good hiking rhythm. I don't use poles all the time, but I'd say that on 80 percent of my day hikes, overnighters, and climbing trips I now carry a pair.
For you, I'd definitely say that lighter is better. The Leki Ultralites ($100 per pair) use very thin shafts and high-tech alloys to cut their weight to 14 ounces a pair, about five to six ounces less than most other poles. Not a huge amount, to be sure, but one that could become significant on a long walk such as a Grand Canyon trip.
As for losing the shock absorption of your Kompressor's, I wouldn't worry too much about it. Most of the benefits of the shocks go to your elbows and shoulders, not your knees. So you're not going to be hurting them any by using a shock-less pole. In any event, I'm skeptical about whether a shock-equipped pole really does that much. I think it's mostly a marketing ploy.
I'd also do what I could to add cushioning to your boots. Take out the stock insoles and add some gel-based inserts such as Sof Sole Gel Inserts ($10) or Spenco Polysorb Gel Heel Cushions (also $10). They'll help cut down the pounding that your feet and legs are apt to take on the canyon descent.