Good news and bad news, the good news is that the installation was successful. The bad news, I never got the serial to work and the 2nd bad news is that I don't know why the installation worked. I was using the latest Rufus to create the USBs and also tried previous versions of it, it's straightforward and when it worked with the Ver. 5 DSM I didn't give it any further thought. After going through the FAQs again I thought I give Win32DiskImager a go, it worked first time and also with all my USB sticks (4G, 8G & 16G, changed VID/PID for each one). Couldn't see any setups in Rufus that may cause the issue, its a mystery which I hate. The only possible reason I can think of is the first 15MB EFI system partition that once created cannot be erased under windows 10 disk-manager but I had to removed it using other third party software otherwise Win32Diskimager would fail when creating the image. Rufus on the other hand doesn't care which could be the problem.
