In short, Creative Labs bought Aureal, and is not releasing the information required to write a proper driver.

Links:
http://www.linux.org.uk/OSS/ Home page of the Linux Sound SubSystem, which Knoppix supports at present. Aureal cards are listed as unsupported.
http://alsa.linux.or.jp/black.html Black list page of the ALSA Project, which is developing the next-generation soundcard support for Linux.

The remaining options would require modifying Knoppix and creating a new master CD.

http://www.opensound.com/osshw.html List of cards supported by 4Front Technology's Open Sound System. The original developer of the Linux Sound SubSystem went on to start this as a business. They list support for the Vortex and Vortex2, but check the README for details. The AU8810 is not supported.
The Open Sound System is designed to be compatible with the Linux Sound SubSystem, but is not free of charge and is not Free -- it may not be legally distributed free of charge. In other words, you can add it to your own Knoppix master, but you can not then give the master away.

http://www.greg.louisville.ky.us/archive/000113.html Greg Loeffler's page on using Aureal's old AU88xx drivers with Linux. Follow his instructions for Debian. Loeffler mentions using the 2.4.18 Linux Kernel; as I write this (January, 2003) Knoppix is using the 2.4.20 Linux Kernel.

Good luck!