Making a custom distro for a D-Link DNS-320

I have a D-Link DNS-320 NAS. It has an OEM linux based OS which is fine but it's a pain to run extra programs. So I would like to try and make my own distro that has the additional programs I want to run. However I have no knowledge of ARM cross-compiling or embedded devices.

The NAS uses U-Boot to start the kernel which I've never used, I've only used GRUB and LILO once by accident.

Since I have no knowledge of making distros for embedded devices I don't know what questions to ask therefore: What suggestions or information do you have that would be useful to me?

Thanks in advance.

Has any of the source been released for it? What about the toolchain/cross compiler? You'll need at least the toolchain before you can go any farther.

Has anyone else made any progress on replacing the firmware image on this device? Or at least, getting it to execute additional binaries?

Originally Posted by MS3FGX Has any of the source been released for it?

Yes but a very old one, the current version is 2.00 and the latest version version whose source is available is 1.00. Maybe I can bug D-Link for the source

Originally Posted by MS3FGX What about the toolchain/cross compiler? You'll need at least the toolchain before you can go any farther.

Okay.

Originally Posted by MS3FGX Has anyone else made any progress on replacing the firmware image on this device? Or at least, getting it to execute additional binaries?

Yes there's Fonz's Fun Plug which I've used but it a bit of a pain to add third party programs. There's this
which shows how to replace the firmware with Debian Linux. Following this how-to requires soldering a serial port on which I'm not comfortable with doing.