If you experience a problem with your rhythms sounding a little lopsided, swingy, or generally not precise, this may have something to do with latency.
"Latency" is a term commonly used in audio software which defines the time from when a note is activated to the time it takes to be heard through your speakers or headphones. Latency settings can have HUGE effects on performance so it's a good concept to get the hang of. If you are running VDL:2 by itself or within Kontakt in stand-alone mode, in the File menu under "Settings" is a "Soundcard" tab. In here (depending on your soundcard) you'll see a slider which allows you to set your latency (measured in milliseconds).
When latency is set at lower values, it places more burden on your CPU. If it's set too high, it will help CPU performance but can cause bottlenecks if you're trying to play back fast rhythms (like open-stroke rolls or fast single-stroke rudiments).
Since each system configuration is slightly different, there is not one "default" setting that we can suggest. However, it's not a bad idea to set latency around 30-40ms as a good starting point. If the CPU is becoming taxed (watch the CPU meter in VDL during playback), you may hear pops, clicks, or audio dropouts. In such cases, you may benefit from increasing latency a little. If your rhythms are sounding wobbly or swingy, your latency may be set a little too high.
Keep in mind, PC users will experience the best latency control when using a soundcard that uses ASIO audio drivers. DirectSound or MME drivers do not perform as well, so using a soundcard with ASIO drivers is highly recommended.
Note for Sibelius users:
In the "Performance" window, check to be sure your Espressivo setting is set to either "meccanico" or "senza espressivo." This will limit the amount of expressive velocity interpretation applied by Sibelius. Higher espressivo settings work pretty well for mallet lines, but with drumline material that requires more precision, lower settings will give you more accuracy.