Welcome and yes, there might be a way to resolve your issue.

Number one, 20X is still a bit too fast for reliable burning. I use 4X and do not have any issues with that. There is ABSOLUTELY no argument with this issue. It's been hashed over many times and the comment is valid. see: http://www.knoppix.net/wiki/Downloading_FAQ You can use the testcd code to see if the cd is readable. That still does not mean it is perfect, just that everything it looked for seems to be there.

Number two, you can use cheat codes to configure how Knoppix boots. There is a "Documentation" link at the top of the page that should have the info you need. Look here: http://www.knoppix.net/wiki/Cheat_Codes "xmodule=radeon" mighty be a good one to start with. Remember to type "knoppix" first and the the cheat codes you want to use. Like "knoppix dma xmodule=radeon" for example. The dma cheatcode would be used in addition to specifying the radeon module in the example. noapic is also a good one. You can try the "failsafe" or "noagp" also. Those are only a few, but might be a good start. dma seems to be one that gets used quite a bit for Knoppix. DMA is off by default in the later versions of Knoppix and some optical and hard drives work better with it turned on.

Good Luck!