One thing you should make sure is that you are using your pro audio card's ASIO drivers, neither Nuendo nor Cubase SX/SL default to the best driver when you first install it. Go to Devices - Device Setup - VST Multitrack, and make sure in the ASIO driver that you have the ASIO driver specifically for your audio card, not the ASIO Multimedia Driver. Simply select the ASIO for (your audio card) and select Switch when asked, and you will be able to use your audio card with much lowered latency, provided your card has ASIO drivers.