I live in Washington too, near Seattle where we get a lot of rain. I feel like the rain likely helps with the poop and smell because it breaks up the poop and washes it into the soil. I could be wrong.
I use sweet pdz, but only inside my ducks' barn room. It does help with the smell. I compost their bedding and the pdz is always broken down by the time I use it in my garden, so I would be really surprised if you couldn't use it in your grass since it is a natural product. I suppose you could test a small area first.
One thing I've noticed is that food can affect the odor of poop. I had to feed one duck a lot of scratch for medical reasons, under the guidance of her avian vet. Her poop was really stinky! My other ducks' (who had a different diet) poop barely had an odor compared. I shared this theory with another BYC member who was feeding scratch and pellets to their ducks, and they discontinued scratch for a week to test it out. Their ducks area smelled a lot better! I've heard some members say that mealworms and high protein can affect the odor.
I feed Mazuri waterfowl, give my ducks tons of space to spread the poop out, and use pdz. I never scoop poop except in the barn and I don't have an issue with smell.
Regarding the quacking, personally I love it and have no nearby neighbors. I have heard that people offer free duck eggs to get neighbors to appreciate ducks in the neighborhood.
I'm happy to hear you are enjoying your ducks!