I have a ReadyNAS Ultra 6. I've installed DSM 4.1 as a VM into VBox running on my ReadyNAS. I also have a QNAP TS-469 Pro that I have install Synology directly by flashing the bios and indirectly by using VBox to install a Synology VM. Flashing the Synology DSM image will overwrite the DOM/SMI bios. QNAP's DOM bios is 512M while ReadyNAS's SMI bios is only 128M. The issue with the ReadyNAS is that the unit's serial number, model name, and capabilities are stored in a hidden file on the ReadyNAS DOM/SMI bios. If the file is erased by a DOM/SMI bios flash, you may not be able to restore its identity without involving NetGear Tech Support. Also, the Synology DSM OS will not be able to recognize the ReadyNAS OLED or buttons. NetGear's drivers are specialized and only support 2.6 series kernels while the Synology OS is 3.x. For both the ReadyNAS Ultra 6 and the QNAP TS-x69 series, I find that it's better to install VBox first then install Synology as a VM. This way you can install ReadyNAS addons through FrontView and Synology addons through its web interface - this gives you the best of both worlds.
Also, I have upgraded my ReadyNAS to a faster CPU and 4G's of memory. I can run Win8Pro in a VM on my ReadyNAS with no problems.
I recommend that you install VBox onto your ReadyNAS and then Synology as a VM. In my opinion, VBox is the future of the ReadyNAS line because you don't need to do much to install many other OS's and NetGear seems to no longer offer any real support.