Matrix Table - Multiple Total Rows

Heres is one way. (I created a dimension table for item)

Create a new independent table using the following code:

Matrix Table =
VAR _item =
    ADDCOLUMNS (
        DISTINCT ( fTable[Item] ),
        "Order", RANK.EQ ( fTable[Item], fTable[Item], ASC )
    )
VAR _Rows =
    COUNT ( 'Item table'[Item] )
VAR _totals = {
    ( "Total", _Rows + 1 ),
    ( "Grand %", _Rows + 2 )
}
RETURN
    UNION ( _item, _totals )

Now you need to create the equivalent following measures for each Quantity value

Sum Q1 = SUM(fTable[Quantity 1])

Sum Q1 All Items = 
CALCULATE([Sum Q1], ALLSELECTED('Item table'[Item]))

and finally for the matrix:

Quantity 1 =
VAR _itmes =
    CALCULATE (
        [Sum Q1],
        TREATAS ( VALUES ( 'Matrix Table'[Item] ), 'Item table'[Item] )
    )
VAR _total = [Sum Q1 All Items]
VAR _Grand =
    DIVIDE (
        [Sum Q1 All Items],
        [Sum Q1 All Items] + [Sum Q2 All Items] + [Sum Q3 All Items]
    )
VAR _rows =
    COUNT ( 'Item table'[Item] )
RETURN
    SWITCH (
        SELECTEDVALUE ( 'Matrix Table'[Order] ),
        _rows + 1, _total,
        _rows + 2, FORMAT ( _Grand, "percent" ),
        _itmes
    )

Add the field from the Matrix Table to the visual and the measures to get:

Sample PBIX file attached