Is there a column in transactionline that provides the net amount of a transaction line item in the company base currency? i.e. converting Euro lines to USD? If this is available, that would save a lot of steps for me in what I need to accomplish

BUILTIN.CONSOLIDATE function I think is what you're looking for. I am consolidating to subsidiary with id 11 is consolidating all currencies to a US based currency that were posted in a foreign see query below

SELECT
    transaction.id,
    transaction.number,
    transactionLine.foreignamount,
    BUILTIN.DF(transactionLine.subsidiary),
    transactionLine.subsidiary,
    BUILTIN.DF(transaction.currency) AS currency,
    TransactionAccountingLine.amount, 
    TransactionAccountingLine.debit, 
    TransactionAccountingLine.credit, 
    BUILTIN.CONSOLIDATE(TransactionAccountingLine.amount, 'INCOME', 'DEFAULT', 'DEFAULT', 11, transaction.postingperiod, 'DEFAULT')

FROM
    transactionLine
    INNER JOIN transaction ON transaction.id = transactionLine.transaction
    INNER JOIN TransactionAccountingLine ON (
        transaction.id = TransactionAccountingLine.transaction
        AND TransactionAccountingLine.transactionline = transactionLine.id
    )
WHERE
    TransactionAccountingLine.posting = 'T' 
FETCH NEXT 1000 ROWS ONLY

you can also use

BUILTIN.CURRENCY_CONVERT(TL.netamount, 4, T.trandate)

to convert to any target currency

These are great suggestions, but the project I am working on uses CData Sync to pull data and we unfortunately are not able to use BUILTIN in our queries. Is there another way to solve this without BUILTIN functions?

Get the exchange rate and calculate on your end

SELECT TOP 1 CR.exchangerate 
    FROM currencyrate CR 
    WHERE CR.basecurrency = C.id AND 
      CR.transactioncurrency = 4 AND 
      CR.effectivedate <= T.trandate
    ORDER BY CR.effectivedate DESC