Where are the exchange gain / loss accounts set, and can I have a one account for gains and a different account for losses?
Yes, it is possible to have a different account for realized foreign exchange gains and losses as well as unrealized foreign exchange gains and losses. The first step is to create those accounts in the General Ledger. The next step is to create the foreign currency bank in Bank Services and assign the Exchange Gain and Exchange Loss accounts on the Currency Tab.
Then designate each type of account in AR Account Sets and AP Account Sets. It is possible to have one set of gain/loss accounts for AP and a completely different set of accounts for AR and another for BK - if that amount of detail is desired.