how to pass a date from a subreport

Hi, 

A client is using the Production Edition. 
The Sales Order lines can be tied to different production orders. 

We are trying to get the earliest start date of the production tickets and print it in the header of the Sales Order. 
I created a subreport that prints the Min ( AMProdItem.StartDate) correctly. I even have it set as a variable that prints $EDate = Min ( AMProdItem.StartDate). These are both printing correctly in the subreport. 

My question is how do I / or can I get the $EDate to be returned? 
When I set the Value as =$subReport1_EDate, I get a zero that prints. 

Or is there a better way to get the earliest start date from multiple production to print on the Sales Order.

Thank you, 
Bill