If you look at the schema browser for Sage 500 you will find the information on the Sales Order records to include the Header, detail, and distribution records. 

Also, you cannot go directly from stgSOLine to tsoSOLine.  It doesn't contain all the information tsoSOLine needs (SurrogateKey for example) and you are skipping any validations on the data.  stgSOLine is part of the Data Import Manager's Import Sales Order process. 

If you are trying to import sales orders into Sage 500, I recommend you try using this first.  If you are not licensed for it, you can still create a process using stored procedure spsoAPISalesOrderIns.  Review this stored procedure and you will see how stgSOLine and the other staging tables are used to create sales orders in Sage 500.  

I would also recommend working with your reseller to assist in the  proper design and the test plan for this process to avoid any possibility of data corruption in the system.

I saw your response "I am using the spsoAPISalesOrderIns stored procedure but it does not indicate to use any other staging table other that StgSOLine in terms of validating the header and details." , but it is not displaying on the website at the moment. 

If you reviewed the stored procedure, you would see it reads records from StgSalesOrder by session and process status.  The detail records in stgSOLine link to the header records in stgSalesOrder by TranNo and Session.  I am not sure where you saw only stgSOLine was used for spsoAPISalesOrderIns.  If you have DMT installed, you can use it to see what staging tables are used for each process or as I suggested previously script the stored procedure and review it to see what staging tables are used and how they relate to each other as well as what values to pass for each parameter of the stored procedure..