Why dont you change your authentication methed from Windows to muxed mode?
And then just creat a SQL user and authenticate it from ePO config page
For Requirdc prrmissions plz follow this KB
due to corporate policy we have to use domain account. ePO was installed with sa rights and after that we switch this account to db_owner. Under this rihts everything is OK. We made application account with no rights but it has access to database under db_owner rights. After switching accounts is ePO unable to connect database (Full SQL server in cluster). After I added application account to Administration group everything is runing with no problem. But this account due to company policy can´t be server local admin. 4.6.x ePO is running with same account with no local admin rights. Only 2 things are different: ePO 5.0 and Windows server is 2012.
Due to connetion to database is problem in "licence expiration" and until we will add user to admin group we are not able to login into localhost:8443/core/config problem is escaleted to platinum support but it should be solved in a new built (during summer).