My quad and bass voices in Kontakt sound distorted when I play them through headphones, internal speakers, and external speakers on my laptop. Do I need to run my sound through an amplifier or is there something else I can do to get a better sound? I am running Sibelius 3 if that matters. Thanks.
You may have turned the instrument's volume up too high within Kontakt. Keep in mind, you can control the volume of each instrument individually within Kontakt, and global volume is handled from your computer's main sound settings. The volume in Sibelius' mixer window can also affect the volume, but if you're hearing distortion, I'm guessing you may have turned up the individual instrument's volume within Kontakt.
Kontakt is currently at version 1.5.3. You might consider updating with Native Instruments when you get the chance.