Goldenpond, I can share what has been working for me, I won't call it advice, as I am still learning also. Air pumped into your pond contains about 20% oxygen. Air produced by plants and planktons is near 100% oxygen I believe. My trout have succesfully wintered two years now with 200 days of ice cover, max ice thickness 37" with seven feet of water below. No aeration, but I removed snow cover within a few days of new snowfall on about 3/4 of the pond. I tried to aerate two winters ago and had problems with airlines freezing. Lower fish densities probably helped with keeping d.o. levels up also. Most ponds around me do not use diffusers in winter, either nothing or top water splashers.
