I think I am getting a sense of it's capabilities are.  The conditional equations are the part I was really not sure about i.e. where the APH, CEC, soil family estimate 'er whatever mixed data types could be used to build equations sets.   Granted, I know historical yield will always be the strongest weighted "main effect" - but I wanted some additional granularity going forward. 

Thanks for all the help.  I sent you an email.