Yes. Or possibly SGD to EUR, EUR to HKD. Any path that Interactive Brokers supports can work, but USD is probably the best one.
Currency loss, no. SGD-HKD direct is a much lower volume currency pair, so bid-ask spreads would be correspondingly higher in that alternative universe. Indeed, your credit card network (Visa, MasterCard, etc.) will do exactly the same thing, especially when the direct currency conversion market is not big enough for their needs. And you do the same thing, presumably. When you work, somebody pays you Singapore dollars for your labor services, and then you take those Singapore dollars and exchange them for coffee, for example. Hypothetically it would be nice if you could exchange your labor services directly for a cup of coffee — wouldn’t that be nice and “efficient”? — but there is no practical financial market for that particular barter exchange. So we have intermediate means of exchange, and in this example it’s Singapore dollars. Likewise, the intermediate means of exchange at IB between Singapore dollars and Hong Kong dollars is the U.S. dollar. (Or some other big currency, perhaps.)
However, there is a broker commission for each leg of the exchange, so the commission is approximately doubled. You’re still vanishingly unlikely to find a lower total currency conversion cost anywhere else, but, comparing IB against itself, that particular currency pair will require double commissions.
