You'd be surprised how much dirt comes up when you do the steam cleaning and Oxy. It's trapped dust and dirt. You'll need something to help lift the dust from your carpet, something to make the dust/dirt not cling to it. You can use plain baking soda, but I just loved how spanking clean the Oxy made my carpets.
If you're worried about the detergents in Oxy (which are mild, by the way), you can get an oxygen cleaner that doesn't have any detergent in it. The only chemical compounds in this version would be sodium carbonate and sodium percarbonate.
This creates hydrogen bubbles to clean (it blasts away stains) and is perfectly safe. The only reason that it shouldn't be ingested directly is because the pH is so high (basic) that it would completely hurt your stomach and tear your insides out when indiluted. But when used in cleaning and it's diluted, it's nothing to be worried of. It's like how vinegar is so acidic. You wouldn't drink a gallon of vinegar because it would hurt your insides straight up or munch on borax (pH basic), but it's good for cleaning. I actually used Oxy rather than use the carpet solution that was being sold alongside the carpet cleaner. The girl behind the counter mentioned that if I had Oxy that I wouldn't need the cleaning solution. I did have a bunch of Oxy at home and I tried it and won't use the carpet solution ever again!