This is just my best guess:
The official package from Synology needs to be modified to be able to run on unofficial hardware.
Also, you need something to emulate the boot loader (like a USB Stick) where the original hardware has this on a chip (i think)..
Hopefully, someone with a lot more experience will be able to make a working DSM 5.0 soon. (It was released two days ago)
In the meantime, you could give DSM 5.0 beta a try as this is the latest working release.