Using ReactiveUI/DynamicData, How to observe changes to properties of items in a SourceList

Each item in the list implements ReactiveObject so I've tried using item.WhenAnyValue().Subscribe() on each individual item before adding it to the SourceList. While this works, it has terrible performance and isn't really practical for my SourceList of 40000 items. Is there any way to observe the SourceList once for changes to properties of any items in the list?