Is it required to load data using 2LIS_03_BX datasource to get initialil stock opening balances...!!

2LIS_03_BX --> This structure is used to extract the stock data from MM Inventory Management for initialization to a BW system.

2LIS_03_BF --> This structure is used to extract the material movement data from MM Inventory Management (MM-IM) consistently to a BW system

2LIS_03_UM --> This structure is used to extract the revaluation data from MM Inventory Management (MM-IM) consistently to a BW system. Contains only value changes, no quantity changes.

Before you can extract data for revaluations to a BW system, you must ensure that the transaction/event key is active.
For this, see the following SAP Notes:
· 353042: How To: Activate transaction key (PROCESSKEY)
· 315880: Missing event control after PI-A installation

Usage of BX datasource is depends on business requirement.

Requirement1: For example data getting pulled from R/3 system. It contains 10 years of History Data.
Business requirement is want to see Inventory / Stocks data for last 2 years only.
In this case, to get opening balances can only get through BX datasource and compress WITH Maker update. after that we can load only last 2 years of historic data using BF & UM datasources and compress WITHOUT Marker update.

Requirement2: For example data getting pulled from R/3 system. It contains 2 years of History Data only and entire data needed from reporting.
In this case, we can use BX to pull opening stock balances and compress WITH Marker update and
Pull BF & UM for 2 years of historic data and compress WITHOUT Marker update. Same as above.

OR

Just Pull entire historic data - stock movements (2 years) using BF and UM datasources and compress WITH Marker update . It creates Opening Balances. In this case no need to Load BX datasource.

How To… Handle Inventory Management Scenarios in BW: https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/f83be790-0201-0010-4fb0-98bd7c01e328

Drop your doubts as comments.... will get back to you....