I've got a Samsung CLP-300 attached to the USB port of an AVM Fritz!Box and addressed as socket://fritz.box in my CUPS configuration.
Some applications print just fine. kpdf from KDE 3.5 is among these. Other applications fail to produce a correct output. I get the impression that these are mostly GTK-based, like Firefox, Thunderbird, Gimp, Inkscape. In those cases, saving / printing the document to PDF and printing that via kpdf is often a viable but annoying workaround.
The error behaviour differs depending on the splix version in use. With splix 1.1.1, the printer prints an error page like this:
SPL-C ERROR - Please use the proper driver
POSITION : 0x0 (0)
SYSTEM : src/xl_image
LINE : 462
VERSION : SPL-C 5.24 06-28-2006
This looks quite a lot like https://sourceforge.net/tracker/index.php?func=detail&aid=1604559&group_id=175815&atid=874746
With splix 2.0.0 I don't get any printout at all. Instead the printer LEDs flash some complicated pattern that most likely is some kind of error code. The code repeats, I'm not sure where exactly it starts. But one period looks like this: "Flash 1Y 7K Flash 1C 5M 4K". "Flash" means all 4 toner LEDs and the status LED light up together. The other elements indicate a number of blinks of a given toner color LED. E.g. "7K" is seven blinks of the black toner LED. I don't know if this code if of any use to you, or if you'd have to be a Samsung engineer to make sense of them.
Let me know if there is anything I can do to investigate the issue in more detail. Having my printer attached over network, it would e.g. be possible to dump network traffic, and even compare it with traffic from official Windows drivers. So let me know what data you need, and I'll try to obtain it.
By the way: splix 1.1.1 used to print most colors way too dark, but 2.0.0 apparently fixed that. Thanks!