Switch statement with two independent selected values

Yeah, worst case you have to define all 9 possibilities. I think I could get something like my initial suggestion working but it would take some tinkering.

If you do go with 9 cases, you can also do it without nesting like this:

Sales LY test =
VAR SelectionSales = SELECTEDVALUE ( 'Sales Type'[Sales Type] )
VAR DateType = SELECTEDVALUE ( 'Date Type'[Date Type] )
RETURN
    SWITCH (
        TRUE (),
        DateType = "YTD" && SelectionSales = "Contract Sales",
            CALCULATE (
                SUM ( 'SAP Sales Daily'[Contract_Sales] ),
                ENDOFYEAR ( PREVIOUSYEAR ( 'Date'[Date] ) )
            ),
        DateType = "YTD" && SelectionSales = "Invoice Sales",
            CALCULATE (
                - SUM ( 'SAP Sales Daily'[Gross_Sales] ),
                ENDOFYEAR ( PREVIOUSYEAR ( 'Date'[Date] ) )
            ),
        DateType = "YTD" && SelectionSales = "WAC Sales",
            CALCULATE (
                SUM ( 'SAP Sales Daily'[Wac_Sales] ),
                ENDOFYEAR ( PREVIOUSYEAR ( 'Date'[Date] ) )
            ),
        DateType = "MoM" && SelectionSales = "Contract Sales",
            CALCULATE (
                SUM ( 'SAP Sales Daily'[Contract_Sales] ),
                ENDOFMONTH ( PREVIOUSMONTH ( 'Date'[Date] ) )
            ),
        DateType = "MoM" && SelectionSales = "Invoice Sales",
            CALCULATE (
                - SUM ( 'SAP Sales Daily'[Gross_Sales] ),
                ENDOFMONTH ( PREVIOUSMONTH ( 'Date'[Date] ) )
            ),
        DateType = "MoM" && SelectionSales = "WAC Sales",
            CALCULATE (
                SUM ( 'SAP Sales Daily'[Wac_Sales] ),
                ENDOFMONTH ( PREVIOUSMONTH ( 'Date'[Date] ) )
            ),
        DateType = "YoY" && SelectionSales = "Contract Sales",
            CALCULATE (
                SUM ( 'SAP Sales Daily'[Contract_Sales] ),
                ENDOFMONTH ( SAMEPERIODLASTYEAR ( 'Date'[Date] ) )
            ),
        DateType = "YoY" && SelectionSales = "Invoice Sales",
            CALCULATE (
                - SUM ( 'SAP Sales Daily'[Gross_Sales] ),
                ENDOFMONTH ( SAMEPERIODLASTYEAR ( 'Date'[Date] ) )
            ),
        DateType = "YoY" && SelectionSales = "WAC Sales",
            CALCULATE (
                SUM ( 'SAP Sales Daily'[Wac_Sales] ),
                ENDOFMONTH ( SAMEPERIODLASTYEAR ( 'Date'[Date] ) )
            )
    )