I followed your instructions and when I'm installing DSM_DS3617xs_23739.pat I get error "Failed to install the file. The file is probably corrupted. (13)"
Any ideas? I tried to redownload DSM_DS3617xs_23739.pat from different sources.
Edit:
I found solution. I switched to DS918+ 1.04B boot image and DSM_DS918+_23739.pat