To oxygenate your wort, before pitching the yeast, you NEED the sintered stone in order to actually infuse the wort. Just putting the O2 into the headspace won't give you much of anything since it's NOT infusing. Get a stone on a stainless wand and connect the regulator up to it via some Bevlex tubing. I've been doing this for a long time now. I adjust the flow level depending on the recipe. Lower ABV batches get about 60 seconds at 1 to 1.5 LPM. Bigger brews get more time and/or more flow to get a solid amount of O2 into the wort for the yeast to use.
Do NOT use an aquarium stone for this. They make stones specifically configured to infuse wort. They are safe for use plus with the correct sized openings.
Get the Yeast book by White and Zainasheff and you'll see why you want to use pure O2 to oxygenate via the sintered stone. Short answer is without the pure O2/stone setup, you're never going to get above 8ppm of O2 in the wort. While that might be OK for low ABV batches, you're doing your brew a disservice (and hindering the yeast) in larger brews.