It is easy to compile (say) 2.6.33 on the kurobox itself
(assuming debian lenny armel is already working)
You will need a suitable kernel configuration for the kurobox pro; mine is a bit long to post here.
Also, I use an initrd for booting, unlike Davy-Gravy's setup that you linked to.
make orion5x_defconfig will use the config in arch/arm/configs as an initial choice.
you can then modify it for your needs with "make menuconfig"
make zImage modules (zImage is created in arch/arm/boot)
you now need to convert the zImage to a uImage (to be the new uImage.buffalo in /boot)
and it must not be bigger than about 1.8MB, otherwise it will not load into memory. (REALLY IMPORTANT)
(Put as much as possible into modules.)
see the part about this inhttp://buffalo.nas-central.org/wiki/Kernel-cross-compile-kurobox-pro
(I myself don't cross-compile, I compile natively on the kurobox pro itself)
make menuconfig # if needed
devio > foo 'wl 0xe3a01c05,4' 'wl 0xe38110e5,4' # For kuropro/lspro
cat foo arch/arm/boot/zImage > zImage.new
mkimage -A arm -O linux -T kernel -C none -a 0x00008000 -e 0x00008000 -n 'linux' -d zImage.new uImage
scp uImage kuro:/tmp/
rm foo zImage.new
This modifies the zImage to make it into a uImage that the kurobox pro can boot by adding a little header string it looks for at the beginning
of the image.
(Of course, if you replace your working uImage.buffalo with the one you just compiled, and the new one won't boot, unless you have serial port console access (to choose which image to boot from) you need to be able to open up the kurobox, and mount the harddrive on some other linux system to put back the old one.....)
Maybe you can practice by first seeing if you can successfully rebuild the older kernel you presumably have a .config for (2.6.25?)