ASIO is a method of directing unmodified sound data to a sound card. The sound card must have a driver capable of accepting ASIO output.
For Vista and above, you may also consider using WASAPI.
ASIO4ALL is a publicly available driver that accepts ASIO output and converts it to Kernel Streaming.
MC playback options must be set to use ASIO.
Here's a thread that may help.
If you experience stuttering problems with ASIO, try changing this setting (introduced in 14.0.48):
- NEW: Added new ASIO option 'Use large hardware buffers (recommended to prevent stutter)' that uses the maximum hardware buffer size instead of the default buffer size, which should help alleviate any stuttering issues. (smaller buffers are only desirable in latency sensitive applications like synthesizers)
Also, consider a search on Interact.