Following variables can be used as KCL parameters at boot time:

slxsrv=     - A list of openslx server
slxbase=    - Base directory for resources, such as the config, config.tgz and addons

For a splash screen during boot following commands have to be appended:
vga=current - Sets the screen resolution 
splash      - triggers the splash screen (module 'splash-openslx' must have been build)
quiet       - don't display kernel messages

For debug shells during stage31 set following option:
debug={1..4}

Level:
4 - Debug shell before Network is up
3 - Debug shell after Network is up and before Configuration is fetched
2 - Debug shell after configuration has been fetched and before stage32 is mounted
1 - Debug shell after stage32 mount and before switch_root

Following a sample pxe-menu entry for a system:

LABEL u1304x64
    MENU LABEL Ubuntu 13.04 x64 Curitiba
        KERNEL http://10.254.221.6/u1304x64/kernel
        INITRD http://10.254.221.6/u1304x64/initramfs-stage31
        APPEND slxsrv=10.254.221.6 slxbase=u1304x64 vga=current splash quiet
        IPAPPEND 3