Is there a way I can set my stream cadence to post every 9 days so I have a continued staggered day of the week send? I only see weekly or monthly options.
And the answer to your question is no, this not possible.
I would use a regular smart campaign flow for this. But if you really want to use an engagement program, you can do this:
Set 7 streams. Each of them having a weekly cast schedule and each of them casting a different day of the week.
Then a smart campaign that monitors email sent. When email 1n 8 or 15 is sent, the campaign waits 3 days and move the lead to stream 2. When email 2, 9, 16 are sent, way 3 days and move lead to stream 3, etc...
Do not be sorry, it happens to everyone at least once
Hence the changes in the community that will be rolled out soon: Improvements In Community – Making Great, Even Better!