Windows 2000 MME and WDM audio drivers has a hard-fast limit of 20 inputs and 20 outputs (10 stereo) in the system. Products such as Cool Edit Pro which use these drivers are subject to this limitation. If you are using an audio application which has the option to use ASIO drivers, you’ll want to choose this option because ASIO is NOT subject to this limitation.
Also, any built-in audio cards such as Crystal Audio, Sound Blaster, AC97, and Sound Max which are enabled will reduce the amount of IO your pro-audio card has available because these count toward the limit of 20, so you’ll likely want to disable these sound cards to get the maximum IO for your pro-audio card.
Windows XP does not have the same limitation- it can accomodate 32 or more inputs and outputs.