As there is no relation between nandina and bamboo, this might not be the most helpful of the Forums to be posting in ("Shrubs" comes to mind as an alternative). I've never had problems growing nandina in the condtions you describe in the PNW, and it's my understanding that nandina like acidic soil.

Here is a link that might be useful: PlantFiles

And you have to put on a ton of lime to change the pH even one point. If you haven't done so already, sample your soil and have it tested before trying to do anymore fiddling with its chemistry. That way you can have a basis for informed action.

Do additional periodic sampling to keep track of the ongoing situation.